Tales of Monitor Lizard Tails and Other Perspectives

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Herpetological Review 50(1), 2019
178178
ZOO VIEW
Herpetological Review, 2019, 50(1), 178–201.
© 2019 by Society for the Study of Amphibians and Reptiles
Tales of Monitor Lizard Tails and Other Perspectives
sinCe i—about 30 years ago—got My First living nile Monitor
and beCaMe aCquainted with his liFe habits in the terrariuM, the
Monitor liZards have FasCinated Me all the tiMe, these ‘proudest,
best-proportioned, Mightiest, and Most intelligent’ liZards as
[FranZ] werner striKingly Called theM.
—robert MerteNs (1942)
Modern CoMparative Methods allow the exaMination oF
the probable Course oF evolution in a lineage oF liZards (FaMily
varanidae, genus varaNus). within this genus, body Mass varies
by nearly a Full Five orders oF Magnitude. the Fossil reCord and
present geographiCal distribution suggest that varanids arose
over 65 Million yr ago in laurasia and subsequently dispersed
to aFriCa and australia. two Major lineages have undergone
extensive adaptive radiation within australia: one evolved
dwarFisM (subgenus odatria, pygMy Monitors), whereas the other
australian lineage (subgenus varaNus) reMained large, and
several oF its MeMbers evolved gigantisM.
—eric r. piaNka (1995)
Monitor liZards adopt CharaCteristiC deFensive postures,
Flattening theMselves FroM side to side and extending their gular
pouChes, presuMably to MaKe theMselves appear as large as possible.
oFten they hiss loudly and FliCK their tongues. big speCies lash
their tails liKe whips with Considerable aCCuraCy. soMe speCies
stand ereCt on their hind legs during suCh displays.
Male Monitor liZards engage in ritualiZed CoMbat, Fighting
over FeMales. larger speCies wrestle in an upright posture, using
their tails For support, grabbing eaCh other with their Forelegs
and atteMpting to throw their opponents to the ground. blood
is soMetiMes drawn in suCh battles. sMaller speCies grapple with
eaCh other while lying horiZontally, legs wrapped around eaCh
other as the roll over and over on the ground. the viCtor then
Courts the FeMale, First FliCKing his tongue all over her and then,
iF she ConCurs, CliMbing on top oF her and Mating by Curling the
base oF his tail beneath hers and inserting one oF his two heMipenes
into her CloaCa. (Male varanids have a unique Cartilaginous,
soMetiMes bony, support struCture in eaCh heMipenes, Called a
heMibaCuluM).
—eric r. piaNka aNd laurie J. vitt (2003)
MaintenanCe oF the existing diversity oF varanids, as well as
Clade diversity oF all other extant liZards, will depend inCreasingly
on our ability to Manage and share beleaguered spaCeship
earth. Current and expanding levels oF huMan populations are
unsustainable and are direCt and indireCt Causes oF habitat loss.
they also Contribute to esCalating rates oF CliMate Change. to
address anthropogeniC habitat loss and CliMate Change, we will
have to MaKe Major Changes in our resourCe use.
—eric r. piaNka (2012)
it is evident that the international pet trade in Monitor
liZards originating FroM southeast asia and the indo-australian
arChipelago iMpaCts a MuCh higher nuMber oF speCies CoMpared to
those involved in the CoMMerCial sKin trade…trade iMpaCt in live
varaNus speCies still reMains poorly understood, given the FaCt
that Field Conservation studies are alMost CoMpletely laCKing,
partiCularly in the tropiCs…Current indonesian legislation
appears nontransparent and inCoMplete to Conserve indonesia’s
Currently reCogniZed 28 Monitor liZard speCies. one Major reason
is that traders, partiCularly those harvesting speCies, next to
ColleCtors and MiddleMen, reaCt highly responsive to luCrative
opportunities whiCh are generated by international deMand…
traders have largely beneFited FroM the pauCity oF inForMation
available FroM the wild. in addition, the CoMplex geography oF
this vast island region together with the taxonoMiC unCertainty
in looK-a-liKe speCies and the laCK oF CapaCity building prograMs,
training Material and guides in the Countries oF origin haMper an
eFFiCient trade Control.
—kocH et al. (2013)
In Babylon in the 3rd millennium B.C., monitor lizards (also
known as varanids and, in Australia, goannas) were beloved by
the chief god, Marduk (the long, split tongue can be recognized in
reliefs). Monitor mummies are known from Egypt and monitors
appear in hieroglyphs; in the late Egyptian era (1st century B.C.)
there were genuine “lizard cults” (Brentjes 1975). Aristotle, in
the fourth century B.C., might have been the first person to
study the anatomy of monitor lizards, most likely the Bengal
Monitor (Varanus bengalensis)—brought back with many other
animal specimens from Alexander the Great’s Asiatic expeditions
(Cresswell 1862). A wonderful representation of an incarnation
of Gautama Siddhartha, adorned with a water monitor’s head,
resides in a Thai Buddhist temple in Bangkok (Fig. 1). Before he
achieved nirvana and became the Buddha, Gautama Siddhartha
JAMES B. MURPHY
Division of Amphibians & Reptiles, National Museum of Natural History,
10th and Constitution Ave NW, Washington, DC20013-7012,USA;
e-mail: murphyjb@si.edu
ROBERT W. MENDYK
Department of Herpetology, Audubon Zoo, 6500 Magazine Street,
New Orleans, Louisiana 70118 USA;
e-mail:rmendyk@auduboninstitute.org
Department of Herpetology, Smithsonian National Zoological Park,
3001 Connecticut Avenue NW, Washington, DC 20008, USA
KYLE L. MILLER
Department of Herpetology, Department of Animal Care Sciences,
National Zoological Park, Smithsonian Institution,
3001 Connecticut Ave NW, Washington, DC 20008, USA;
e-mail: millerkl@si.edu
LAUREN AUGUSTINE
Saint Louis Zoo, One Government Drive, St. Louis, Missouri 63110, USA;
e-mail: laugustine@stlzoo.org
Department of Herpetology, Smithsonian National Zoological Park,
3001 Connecticut Avenue NW, Washington, DC 20008, USA

Herpetological Review 50(1), 2019
179179
was the Bodhisatta of Many Lives. Legend has it that in one of
these lives the Bodhisatta, who was born as a lizard. His life was
that of a lizard along a river, hunting for food and basking in the
sun, ōwhich sounds like a pretty nice lifestyle to us.
Monitor lizards have proven to be interesting subjects
for behavioral studies. H.-G. Petzold (1984, translated from
German) stressed the importance of observations made on
monitors in captivity. “In appropriately equipped large terraria—
or in climatically favorable regions, held in outdoor enclosures,
monitors are impressive show animals and biologically
interesting study objects at the same time. Their care in zoos
goes back to the times of the menageries; only a few decades ago,
successful breeding was among the rarest of zoo events. A large
part of our knowledge about the behavior and reproduction of
individual species of the genus Varanus is based on terrarium
observations.” At the Smithsonian National Zoological
Park (SNZP), a female Komodo Dragon (V. komodoensis)
demonstrated play behavior, interacted with inanimate objects
and human caretakers (Burghardt et al. 2002; Murphy and Walsh
2006). A recent study by Loh et al. (2018) summarized the state of
peer-reviewed research in AZA zoos and aquariums.
A sizeable threat to smaller Australian varanids is the
invasive Cane Toad (Bufo marinus = Rhinella marina), that has
expanded its range across the top half of the country. One of the
most disastrous examples of human miscalculation has been
the introduction of these highly toxic anurans into the sugar
cane fields of Queensland in 1935 to control invertebrate pests.
However, the Yellow-spotted Goanna (V. panoptes) is a large (up
to 1.5 m TL) monitor inhabiting woodlands and floodplains
in New Guinea and northern Australia. Ujvari and Madsen
(2009) radio-tagged nine lizards to investigate predation on the
toads; they discovered > 90% mortality in the study area due to
ingestion of toxic toads.
The introduction of two invasive mammal predators—
European Red Fox (Vulpes Vulpes) and feral House Cat (Felis
catus)—in Australia has resulted in direct and indirect mortality
of goannas. Both foxes and cats kill monitors, and these alien
predators are also responsible for the widespread use of poisoned
baits to control their populations. There is a critical need to
instruct land managers to properly use bait products. Jessop et al.
(2013) studied bait effects on Lace Monitors (V. varius) and found
that these lizards can remove and ingest surface-laid Curiosity©
baits. Depending on daily weather conditions, up to 22% of baits
per day were removed by varanids during the summer.
A study by Woinarski et al. (2018) listed astronomical numbers
of reptiles killed by feral cats. These figures are sobering and
disquieting: feral cats in Australia’s largely natural environments
kill more than one million reptiles per day, and individual cats
take, on average, more than 225 individual reptiles each year,
with almost all of these being native species:
“the loss oF ~1.8 Million native reptiles per day due to
predation by Cats provides Further evidenCe oF the potential
Conservation iMpaCt oF this introduCed predator on australian
biodiversity, and undersCores the value oF eFForts now being
Made to Manage Feral Cat populations (e.g. through loCal-sCale
exClosures, enhanCed island bioseCurity, broad-sCale predator
Control prograMs) and the predation pressure they exert (e.g.
ManageMent oF Fire and graZing pressure), espeCially targeting
Conservation ManageMent For speCies whose population viability is
Most vulnerable to Cat predation.”
Woinarski has also published studies on native birds and
mammals, mirroring the results shown for reptiles. The effects
of feral cats on local goanna populations can be significant. For
example, Sweet (2007) had six of 50 radio-tracked Spotted Tree
Goannas (V. scalaris) and Black-headed Monitors (V. tristis) at his
study site in Kakadu National Park, NT, that were predated by a
single feral cat, and observed several additional cases of feral cat
predation on non-tagged individuals. Nutt (2011) listed Varanus
sp. as among the 20 most important prey categories of feral cats
in north-central Queensland.
We have listed many excellent papers concerning varanids in
the Literature Cited: Rotter (1963), Minton and Minton (1973),
Auffenberg (1981, 1994, 1998), Pianka (1986), Pianka et al. (2004),
Pianka and Vitt (2003), Bennett (1998, 2003), Burden (1927),
King and Green (1993, 1998, 1999), Surahya (1989), Vincent and
Wilson (1999), Murphy et al. (2002), Rogner (2007), Eidenmüller
(2007, 2016), Swan (2009), Lenz (1995), and Brown (2012). In
the series Mertensiella, a supplement to Salamandra, Wolfgang
Böhme and Hans-Georg Horn edited a volume called Advances
Fig. 1. Thai Buddhist temple representation of an incarnation of Gau-
tama Siddhartha, adorned with a monitor’s head. The story began
in India, where Buddha had been a Bengal Monitor. We believe that
the monitors on either side are likely V. bengalensis and the scene is
in a Buddhist temple in Bangkok, Thailand. The only other species it
could be is V. salvator; however, because water monitors are despised
in Thai culture (the Thai word for them - ‘hîia’ is one of the most de-
plorable insults you can call someone), we suggest that V. bengalensis
is a more appropriate fit.
PHOTO BY PRAWAT THANANITHAPORN AND INFORMATION BY JESSICA AMANDA SALMONSON
Fig. 2. Bengal Monitor (called Lacerta Dracæna) from “General Zool-
ogy or Systematic Natural History. Volume III. Amphibia” by George
Shaw (1802).

Herpetological Review 50(1), 2019
180
in Monitor Research (1991). Two additional edited volumes of
Advances in Monitor Research were produced in 1999 (Horn and
Böhme) and 2007 (Horn et al.). Recently, proceedings from the
Interdisciplinary World Conference on Monitor Lizards held in
Bangkok, Thailand in 2015 have been published by Michael Cota
(2016).
Early artistic renditions often show varanids and other lizards
with coiled tails held over the body, a position now known to be a
bit of an exaggeration (see Shaw 1802; Fig. 2). Many illustrations
of reptiles beginning in the 15th century are not terribly accurate,
perhaps because the artists may not have viewed living examples
and updated technology (engravings, etchings, lithographs,
and so on) was not available at the time. Dennis and Adler
(2003) traced the evolution of herpetological art and improving
technologies for showing amphibians and reptiles. An historical
overview of varanid illustrations is in preparation for the journal
Biawak (see Mendyk et al. 2016).
tail use
The degree of variation and specialization in tail morphology
across monitor species is remarkable. Bedford and Christian
(1996) studied the relationship between tail morphology and
habitat in monitor lizards. Wide ranges of fascinating uses of the
tail have been recorded. One of the most dramatic examples of tail
use is that of male Pygmy Mulga Monitors (V. gilleni) embracing
conspecifics in an arching posture during combat rituals at
the Dallas Zoo (DZ) (Murphy and Mitchell 1974; Carpenter
et al. 1976; Radcliffe and Murphy 1983; Figs. 3–4). Aquatic,
semiaquatic, rock-dwelling, and terrestrial varanids utilize
ritualized combat to establish dominance with conspecifics.
A few examples reflect differences in combat between species
from different habitats. Davis et al. (1986) recorded ritualized
combat in captive Dumeril’s Monitors (V. dumerilii). Honegger
and Heusser (1969) contributed an analysis of the behavioral
inventory of the Asian Water Monitor (Varanus salvator). Horn
et al. (1994) provided a description of the four or five elements
comprising varanid combat:
We think
i
t appropriate to combine these single elements to the
following
four or five phases:
Display phase: aggressive tongue-FliCKing, body
Flattening.
encompassing phase: CoMbatants enCoMpassing eaCh other
with latera
l
display,
part
l
y aCCoMpanied by head jerKs.
clinch phase: bipedal stanCe
i
n wrestling pose with Mutua
l
eMbraCe.
catch phase: tilting over eaCh other and tw
i
sting and
turning around to aChieve
the superior position.
subpressive phase: aFter the Fight Mounting the inFerior
speCiMen (pseudoCopulation), biting (and Chasing iF
i
t retreats).
the Following varanid speCies have been observed to Carry
out ritual CoMbat or enCounters interpreted as suCh: varaNus
albigularis (branCh 1991), v. b. beNgaleNsis (deraniyagala 1957),
auFFenberg 1981), v. duMerilii (davies et al. 1986), v. flavirufus
(thoMpson et al., in press, as v. gouldii), v. gouldii HorNi (this
paper), v. gouldii rubidus (bennett 1992), v. iNdicus (MCCorn &
hensley 1989), v. koModoeNsis (horn 1985), v. MerteNsi (greer
1989; this paper), v. Niloticus (CleMents 1968, branCh 1991),
v. olivaceus (auFFenberg 1988), v. salvator MarMoratus (gaulKe
1989), v. s. salvator (honnegger & heusser 1969, vogel 1979a, b,
rese 1986), v. speNceri (waite 1929; not v. gigaNteus: horn 1981),
v. varius (worrell 1963, breeden & breeden 1972, horn 1980,
twigg 1988, and this paper); FroM the odatria seCtion oF varaNus
have to be added: v. caudoliNeatus (thoMpson et al., in press),
v. gilleNi (Murphy & MitChell 1974, Carpenter et al. 1976), v.
seMireMex (horn 1985), v. siMilis (horn 1985; this paper), and
v. tiMoreNsis (horn 1985). it is iMportant to note that Monitors
show their agonistiC behavioural inventory not only in the Field
under natural Conditions, but also in the laboratory; when Kept
properly, aFter Many years. even Captive-bred speCiMens (e.g. v.
siMilis, see above) display it. thereFore, the inherited nature oF
these stereotyped behavioural patterns is proven.
Rock-dwelling Ridge-tailed Monitors (V. acanthurus) at Dallas
Zoo (DZ) used the spiny tail to wrap around human fingers
when held. In one case, the monitor also bit the space between
Fig. 3. The videotaped sequence of actions during arching bout of
two Varanus gilleni males at Dallas Zoo. From Carpenter et al. (1976).
Fig. 4. Komment-Kampf or ritual struggle of male Varanus gilleni at
Dallas Zoo. A) First sequence, prior to contact. B) Second phase, now
in combat. C) Each male either inflates body with gular pumping
motion and rotates upon longituinal axis or deflates trunk in order to
overpower rival. D) Struggle concludes with winning male on left bit-
ing subordinate loser. Because these lizards were kept in a relatively
small enclosure, the subordinate could not flee and became immo-
bile. The dominant male switched from aggression to courtship be-
havior and attempted copulation. From Murphy and Mitchell (1974).

Herpetological Review 50(1), 2019
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two fingers with surprising force and held this position for ca. 15
min, causing considerable pain. The tail may have been used to
position the bite. Auffenberg (1994) recalled a V. acanthurus that
drew blood from his index finger by forcefully pushing its spiny
tail scales against the finger after it was jammed into the captive’s
burrow. Horn (1999) observed captives using their tails to probe for
prey under rocks. The enclosures at DZ had many flattened rocks
that accommodated small rodent and invertebrate prey hiding
from the monitors; the use of the tail as a probe was never seen
(Fig. 5). Wilson and Knowles (1988) described tail use to block the
entrances to burrows, presumably as a defense against predators.
Sprackland (1980) described peculiar tail use in a captive
Storr’s Monitor (V. storri):
"i had been siFting the sand in the Cage and pulled the Male
liZard out FroM under his retreat. onCe exposed, he Moved a short
distanCe away FroM My hand, Flattened the body to FaCe Me, and,
with nose in the sand and hips upraised, began to rattle the tip oF
his tail. the latter third oF this organ would be rapidly vibrated
in a series oF 2–3 seCond bursts, until i withdrew My hand. later
observations showed that this display would be invoKed when
another liZard enCroaChed upon the Male’s perCh, or, when
intiMidated by Me or large prey iteMs. iF the vibrating tail CaMe
into ContaCt with any solid Material (roCKs or twigs), the sound
produCed was a distinCt buZZ, siMilar to that produCed by young
rat and bull snaKes (elapHe sp. and pituopHis sp., respeCtively)."
Sprackland also noted that when manually restrained, a V.
storri forcefully rubbed the spines of its tail against his hand,
slightly abrading his skin.
Patanant (2012) described tail-probing behavior in a King’s
Monitor (V. kingorum) and listed three other literature accounts
describing this behavior in other varanid taxa (Gaulke 1989;
Eidenmüller 1993; Horn 1999). Patanant (2012) recorded that
prey is located using vision and/or olfaction. If the crevice is too
narrow for the lizard to enter with its head, the lizard forms a
semicircle with its body and rapidly undulates the tip of its tail
to force the prey item out of its hiding spot. When fleeing the
hiding spot, the prey is chased and consumed.
Members of the tree monitor, or V. prasinus species complex,
have long prehensile tails measuring twice the length of the body
and are used to assist with climbing and descending from trees.
Emerald Tree Monitors (V. prasinus) may hang from branches by
the prehensile tail tip and lift prey such as rodents held in their
jaws from the substrate. In the Dampier Peninsula Goanna ( V.
sparnus), the tail is highly prehensile, similar to that of the Short-
tailed Pygmy Monitor (V. brevicauda), possibly functioning to
assist in navigating through Triodia clumps (hummock-forming
bunchgrass) and shrubs (Doughty et al. 2014).
In several larger species, the tail can be used as a powerful
whip-like weapon for defense. Stirling (1912) referenced claims
made by Australian anthropologist Francis James Gillen that
he once saw a large Perentie (V. giganteus) use its tail to knock
down an aboriginal woman with a powerful blow to her legs. He
also mentioned a third-hand account of both forelegs of a dog
being broken in a similar manner. Mitsch (1936) reported that an
irritated V. varius broke the glass window of its terrarium with a
blow from its tail. Kent-Seville (1897) noted that a zookeeper at
Regents Park sustained severe lacerations to the neck from the
tail of a V. varius as he attempted to clean its enclosure. At DZ,
when three adult Crocodile Monitors (V. salvadorii) were placed
on the floor, all three lizards accurately used the long tail tip to
strike at JBM’s eyes. In several cases, his eyes were nearly struck
so he started using a welder’s mask to avoid injury. [As an aside,
these lizards regularly showed blood and saliva in the labial
region and dental arcade. At first, it was interpreted as a medical
issue but there were no outward signs of pathology. Examination
of published photos of captive lizards indicated that this was a
regular occurrence, so we speculated that this condition might
be similar to the exudate from mouths seen in Komodo Dragons.
This phenomenon is frequently seen in captives of species
with exceptionally long teeth—e.g., V. salvadorii, V. doreanus, V.
yuwonoi—and might be related to normal tooth replacement (S.
Sweet, pers. comm.).]
The laterally compressed tails of semi-aquatic species such
as Mertens’ Water Monitor (V. mertensi), the Nile Monitor (V.
niloticus), and V. salvator allow for powerful swimming but
can also aid in sequestering food. A V. mertensi at SNZP used
its laterally compressed tail to corral live feeder cichlids into
the shallows of a smaller pool that had a rock perimeter. This
monitor chased the fishes from the larger pool into the smaller
one where they were more vulnerable. The tail was pressed into
the spaces between rocks separating both pools or raised above
the rocks to trap the fishes. Some of the fishes leaped over the
monitor, who caught them in mid-air in many cases (JBM, pers.
obs.). This behavior has been observed in other captive (Vincent
and Wilson 1999b) and wild V. mertensi (Hermes 1981), and has
also been documented in wild V. niloticus (Keith and Ginsburg
2010). Mayes et al. (2005) observed a V. mertensi at an irrigation
channel drain in East Kimberly in Western Australia during the
late wet season. The monitor was standing on the edge of an
artificial waterfall and snatched three fish out of the air. In Sri
Lanka, Wikramasinghe et al. (2010) observed a V. salvator using
thrashing tail movements to displace water and small fish from
small shallow pools during the dry season, where they were
easily captured and consumed on land.
Christian (1981) described a truly remarkable positioning of
the monitor tail:
one habit oF the blaCK-headed Monitor [varaNus t. tristis]
that helps distinguish it FroM other Monitors (partiCularly at
a distanCe) is its tendenCy to Curve the long tail in a high arC
over its head while sunbaKing. i have never seen [this] in any
Fig. 5. Illustration of Odatria ocellata now V. acanthurus from “The
Lizards of Australia and New Zealand” by John E. Gray and Albert
Günther from 1845 to 1875. The spiny tail seems to be used to block
entrances to burrows. This publication was reissued by SSAR in 1995.

Herpetological Review 50(1), 2019
182
other speCies oF Monitor, inCluding the FreCKled Monitor [v.
tristis orieNtalis], resting in this Fashion. this ClassiC posture is
Followed by an aMaZing burst oF speed as the liZard is approaChed
and in a Flash it has disappeared aMongst the spiniFex.
This behavior was observed in juvenile V. tristis orientalis in
captivity (McDonald 1999).
McDonald (1999) also observed tail-luring behavior in
captive-bred hatchlings of this species, as well as an individual
that used its tail to flick a cricket off branches inside its enclosure.
Varanus tristis have been reported to use their tails to rustle leaf
litter and stir up small skinks and insects so they could then be
seized (Sweet 2007); this behavior has also been observed in
captive specimens of the Kimberly Rock Monitor (V. glauerti)
(RWM, pers. obs.).
Lizard ecologists can often create indirect behavioral profiles
by examining tail markings in the substrate. In the Desert
Monitor (V. griseus), Michael Stanner (in Pianka et al. 2004) listed
indirect communication by spoor:
"while running Fast, the Monitor raises its body and leaves
only Footprints. oCCasionally the tail May slightly touCh the
sand, leaving a short straight traCtion MarK; 2) while walKing or
running slowly, the Monitor leaves a sinuous traCtion MarK oF the
tail with Footprints on both sides; 3) aFter deFeCation, v. griseus
wipes its CloaCal region in the sand, leaving a broad traCtion
MarK. during this aCt, the Monitor propels itselF Forward with
the ForeliMbs only. the hindliMbs are raised and do not touCh
the sand; 4) tsellarious and MensshiKov (1994) Coined the terM
‘drag’ For the Fourth type oF traCtion MarK. the Monitor presses
its tail and/or its CloaCa and hind part oF the belly into the sand
and leaves a distinCt MarK oF up to 10 M long, using all Four liMbs
to propel itselF Forward."
If the trail is several hours old, the male can track the female
in the right direction; if several days old, it is hit-or-miss. Farlow
and Pianka (2000) described variation in the trackway patterns
of Australian desert-dwelling monitors, noting that different
species left their own conspicuous tail drag-marks.
threat and deFensive behavior, MiMiCry
An adult V. mertensi was placed in a mixed lizard exhibit at
DZ that housed several West Indian Iguanas (Cyclura) to see if
they would be compatible. The monitor immediately assumed a
threat posture that was described by Murphy (1969) and Murphy
and Lamoreaux (1978).
Tsellarius and Tsellarius (1997) described threat behaviors of
V. griseus during encounters with conspecifics:
"Fights were rarely noted and only between unFaMiliar
liZards. it is proposed that ritual CoMbat arises FroM displays
oF doMinanCe and not FroM a ritualiZation oF the Fight. the
behavior oF Monitors during ContaCts is highly varied and not
stereotypiCal. data FroM observations attests to the existenCe oF
a CoMplex, MaMMal-liKe soCial struCture in the population."
Bels et al. (1995) provided a threat analysis of V. griseus:
"the threat behaviour in varaNus griseus was investigated
WitH HigH‐sPeed CineMatograPHy and x‐ray FilMs. lizards exHibit
threat display involving throat MoveMents and assoCiated throat,
thorax and Mouth MoveMents. the FunCtional anatoMy oF the
buCCo‐PHaryngeal region is desCribed and tHreat disPlays are
KineMatiCally studied and FunCtionally interpreted."
Johnson (1976) published the following observations seen in
captive monitors:
"the adult Male v. gouldii (s-v length 91.0 CM) deMonstrated
a high degree oF aggressiveness and displayed the CharaCteristiC
threat posture with baCK arChed, neCK and throat inFlated, and
at tiMes rapidly inFlated and deFlated the body. loud hissing
and rapid tongue FliCKing always aCCoMpanied suCh behaviour.
oCCasionally aFter this initial threat display, rapid tail vibration,
inCreased tongue FliCKing, hissing and bipedal (rearing up on the
hind liMbs) stanCe was assuMed. the author has also observed this
latter bipedal stanCe with extreMe harassMent in Captive v. varius
and v. speNceri. at tiMes the tail was used deFensively in a whip-
liKe aCtion. oFten the v, gouldii aFter assuMing the bipedal stanCe
lunged Forward at the investigator. these latter responses were
only eliCited when Cornered and highly agitated. when grabbed v.
gouldii oFten disCharged the CloaCal Contents and atteMpted to
Claw and bite."
Cota and Krebs (2015) proposed that newly hatched V.
dumerilii, which have bright red heads and glossy black bodies
with creamish transverse dorsal bands, may use Batesian
mimicry to avoid predation by raptors and mammals. There are
several highly toxic red, orange, and yellow-headed venomous
elapid snakes in the geographic range of this lizard—King Cobra
(Ophiophagus hannah), Red-headed Krait (Bungarus flaviceps),
and Malaysian Coral Snake (Calliophis bivirgata flaviceps)—
which might well be the models. The non-venomous Red-headed
Reed Snake (Calamaria schlegelii) may also be related to this
mimicry complex, and the Red-headed Pipe Snake (Cylindrophis
ruffus) conceals its head among body coils, flattens the tail and
arches it upward to display its red pattern, mimicking that of
coral snakes.
When captured and physically restrained, some monitors
appear to use defecation as a defense strategy. RWM recalls an
unfortunate incident involving the late varanophile Mark K.
Bayless, in which he brought one of his White-throated Monitors
(Varanus albigularis albigularis) to the veterinarian for an
examination. While restraining the animal and holding it out
vertically for the veterinarian to inspect its dorsum, the irritated
monitor forcefully evacuated the contents of its bowels, spraying
liquefied feces onto Bayless’ face and into his open mouth.
therMoregulation
One recent development in maintaining captive monitors
successfully is recognition of the need to provide broad thermal
gradients with high surface basking temperatures (Mendyk et al.
2014). Christian and Weaver (1996) examined thermal profiles in
four species of Australian varanids:
"abstraCt: the aiMs oF this paper are to CoMpare the therMal
eCology oF Four speCies oF varanid liZards that oCCupy a range oF
habitats and CliMatiC regions, and to assess the eFFiCaCy oF Methods
For evaluating the extent to whiCh eCtotherMiC aniMals exploit
their therMal environMents. hertZ et al. (1993) have proposed
several indiCes oF therMoregulation, and these are evaluated with
respeCt to our data FroM varanid liZards. the therMoregulatory

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183
CharaCteristiCs oF three tropiCal Monitor liZards (varaNus
paNoptes, v. gouldii, and the seMiaquatiC v. MerteNsi), and the
teMperate-Zone v. roseNbergi were studied throughout the year.
radioteleMetry was used to Measure the body teMperatures (tb’s)
oF Free-ranging aniMals, and MiCroCliMatiC data were ColleCted to
deterMine the range oF possible tb’s that an aniMal Could aChieve.
operative teMperatures (te’s) were estiMated by biophysiCal
Models For eaCh set oF aniMal CharaCteristiCs and MiCroCliMatiC
Conditions. the tb’s seleCted by aniMals in a laboratory therMal
gradient were used to deterMine the set-point range oF tb’s that
the aniMals voluntarily seleCt."
Bartholomew and Tucker (1964) outlined the effects of size,
body temperature, thermal conductance, oxygen consumption,
and heart rate in Australian varanids, emphasizing physiological
differences in size rather than species given that varanids have
roughly the same body plan across taxa. Two important papers
by Mendyk et al. (2014, 2016) concern thermal husbandry of
varanids and should be consulted by those who maintain these
lizards in captivity. Walsh et al. (1999) compared dramatically
differing thermal preferences in wild and captive V. komodoensis
at SNZP. They hypothesized that the life style of captives is less
energetic than in their wild counterparts.
reproduCtion
Of the 80 or so species of varanids currently known to science,
at least 65 have been maintained in captive collections and of
these, around 50 species have successfully reproduced at least
once in captivity. Horn and Visser (1989) reviewed reproduction
of 20 species in captivity and data on their biology (1991; Fig.
6). Horn and Visser (1997) also provided an updated account
on reproduction that covered behavior, diet, egg incubation,
light, reproduction, sexing, and taxonomy. Mendyk (2012)
presented reproductive data for 12 species of monitors kept at
the Bronx Zoo over a 33-year period, including five species that
were successfully hatched at the zoo. Brotzler (1965) outlined
the breeding of V. mertensi in in the Wilhelma Zoo in Stuttgart,
Germany. This species later reproduced on several occasions
at the Bronx Zoo through the late 1990s and 2000s (Lee 2000;
Lee and Friedman 2000; Mendyk 2012). Müller (1970) bred V.
salvator at the Leipzig Zoo, David (1970) at the Ahmedabad Zoo,
and Hairston and Burchfield (1992) at the Gladys Porter Zoo in
Brownsville, Texas. Herrmann (1999) documented husbandry
and captive breeding of V. salvator in the Cologne Aquarium at
the Zoo. At the Frankfurt Zoo, Wicker et al. (1999) kept and bred
the beautiful Cuming’s Water Monitor (Varanus cumingi); this
species was recently bred by the Cologne Zoo (Anonymous 2017;
T. Ziegler, pers. comm.). Ziegler et al. (2009) documented the
first captive breeding of the Blue Tree Monitor (V. macraei) at the
Plzen and Cologne Zoos, and Ziegler et al. (2010) described the
first F2 breeding of the Quince Monitor (V. melinus) at the Cologne
Zoo. Wesiak and Koch (2009) reported on the husbandry, first
breeding, and juvenile development of Rennel Island Monitors
(V. juxtindicus). De Zeeuw (2010) described husbandry and
reproduction of V. glauerti in captivity. The Dallas Zoo hatched
one Butaan (V. olivaceus) in 1992 that died shortly after hatching
(Card 1995), perhaps due to a congenital heart defect. More
recently, the Los Angeles Zoo has experienced repeated success
in reproducing this species (Recchio 2016). Mendyk (2015c,
2016, 2017, 2018) prepared annotated bibliographies on captive
reproduction in several Varanus subgenera.
Brown (2009) recommended using hemipenial trans-
illumination as a sexing technique in varanids. Recchio and
Kasielke (2017) described a successful blood collection technique
for sex determination of incubating V. komodoensis eggs at Los
Angeles Zoo. Judd et al. (1977), Morris and Alberts (1996), and
Morris et al. (1996) explored sex determination in V. komodoensis
and V. albigularis at San Diego Zoo.
The Gembira Loka Zoo in Jogjakarta, Indonesia has
successfully bred V. komodoensis for many years, producing
well over 100 hatchlings (Walsh et al. 1998). The offspring are
maintained in large groups in movable enclosures and are placed
in sunlight daily (Busono 1974). Gaulstaun (1973) reported
that V. komodoensis eggs were deposited in the Zoological and
Botanical Garden of Jakarta, Indonesia; Osman (1967) prepared
a note on the breeding behavior of V. komodoensis at Jogjakarta
Zoo; and Sunter (2008) at London Zoo. Walsh and Rosscoe (1993)
and Walsh et al. (1993) reported on the history, husbandry, and
breeding of V. komodoensis at SNZP. Birchard et al. (1995) followed
oxygen uptake in these V. komodoensis eggs and the energetics
of prolonged development. In 2006, Phillip et al. described
parthenogenesis in V. komodoensis at London and Chester Zoos:
"this reproduCtive plastiCity indiCates that FeMale KoModo
dragons May switCh between asexual and sexual reproduCtion,
depending on the availability oF a Mate — a Finding that has
iMpliCations For the breeding oF this threatened speCies in
Captivity… it oCCurs in Captive snaKes and has been iMpliCated in
one otHer sPeCies‐ argus Monitor lizard (varaNus paNoptes)."
Parthenogenesis has now been observed in at least seven
species of Varanus (Lenk et al. 2005; Konáš 2007; Hennessy
2010; Weichmann 2012; Hörenberg 2013; Grabbe 2014; Grabbe
and Koch 2014; RWM, unpubl.). Additionally, given its apparent
prevalence in captive varanids, an older case of suspected
delayed fertilization in Gould’s Monitor (V. gouldii) at DZ (Doles
and Card 1995) might have been a case of parthenogenesis.
Perry et al. (1993) described the first captive reproduction of
V. g. griseus at the Research Zoo of Tel Aviv University in Israel
(Figs. 7, 8). Visser (1981, 1985) provided notes on the breeding
of V. albigularis and the Yellow Monitor (V. flavescens) in
Rotterdam Zoo. Bosch (1999) bred V. prasinus in the Löbbecke
Museum + Aquazoo, Düsseldorf (Germany). Barker (1984)
Fig. 6. Varanus albigularis in John Anderson’s “Zoology of Egypt”
in 1898.

Herpetological Review 50(1), 2019
184
reproduced Biak Tree Monitors (V. kordensis) at DZ. Boyer and
Lamoreaux (1983) and Horn (1978) bred V. gilleni; Husband
(1991) bred this taxon at the Australian Reptile Park. Mitchell
(1990) reported on the reproduction of V. gouldii, and Card
(1994) reported double clutching in V. gouldii and V. olivaceus at
DZ. Radford and Paine (1989) hatched five V. dumerilii and one
Black Tree Monitor (V. beccarii) at Buffalo Zoo in 2005. Fisher
(2012) described husbandry and reproduction of V. beccarii.
Irwin (1996) described courtship, mating and egg-deposition
by V. giganteus at the Queensland Reptile and Fauna Park (now
Australia Zoo) and DZ (W. Card, pers. comm.). Rehák (1996)
followed the reproductive biology of the Mangrove Monitor (V.
indicus) in Prague Zoo; several important studies on the biology
of this species have resulted from the captive-bred individuals
hatched at this zoo (Frýdlová et al. 2011; 2013a,b; 2017a,b;
Frynta et al. 2010; Gregorovicova 2012). Wicker (1993) presented
reproductive data on V. acanthurus at Frankfurt Zoo. Stirnberg
(1997) described care and breeding of V. varius in Bochum Zoo
that led to 2nd generation offspring.
A number of varanids lay eggs in termite mounds (Green et
al. 1999):
'the internal teMperature oF terMitaria oF NasutiterMes
exitiosus, the Mound speCies used by v. roseNbergi, is Maintained
by the terMites at around 30°C For Most oF the year, but shows
a Mid-winter deCline to around 20°C…in addition, huMidities
are high throughout the year…there is a proteCtive earthen
outer wall that is CoMparatively soFt and Friable, but about 10CM
beneath the Mound surFaCe there is an extreMely hard inner layer
oF Material (about 14CM thiCK) that is diFFiCult to penetrate…on
the inner side oF this layer are the warM nursery galleries, and
these Consist oF a FlaKy Material that is easily broKen."
Kirshner (2016) described various aspects of the termite
mound nesting biology of Rosenberg’s Monitor (V. rosenbergi).
Carter (1999) described nesting and evidence of parental care by
V. varius. Varanus varius lay eggs in the center of mounds. The
eggs incubate within the mound for about 290 days and hatch
in mid-spring. At hatching, the adult (probably the female)
digs into the termite mound to release the hatchlings. What is
remarkable is that the adult remembers the location of the eggs
after ca. 8 months.
At DZ, a pair of V. varius were observed courting, followed
by copulation. The male slowly followed the female until she
stopped moving, then began scratching her dorsum with his
foreclaws. After this behavior, which lasted about 5 min, he
straddled her and twisted his tail to align their cloacae and
inserted the hemipenis. Copulation lasted about 15 min. No
eggs were produced. Complete descriptions of the reproductive
biology of captive V. varius were published by Kirshner (2007)
and Horn (1991).
Eidenmüller and Wicker (1991) covered captive breeding,
artificial egg incubation, development and surgical removal of
impacted eggs in Varanus similis at Frankfurt Zoo. Stefani (2008)
outlined husbandry protocols and reproduction of the Peach-
throated Monitor (Varanus jobiensis) in captivity (earlier referred
to as V. karlschmidti). Jackson (2005) outlined history, natural
history, captive breeding, and husbandry in the Rusty Monitor
(V. semiremix).
interaCtions with huMans
In 1942, Gustav Lederer published observations on captive
V. komodoensis at Frankfurt Zoo, including a photograph of a
woman with a large dragon. Lederer discovered that dragons
are able to distinguish one person from another. At this zoo, the
dragon knew the veterinarian after the second treatment and
could no longer be persuaded to leave its hiding place when the
vet appeared. The lizard even recognized the operating table and
fled from it (Lederer 1931). He described the habits of this tame
dragon that lived at the Frankfurt Zoo between 1927–1944. It was
taken on long walks through the zoo by the director. The dragon
was in excellent health up to its death from an Allied bombing
raid in which the facility was demolished, thus living 16 years,
8 months, and 21 days. At DZ, curator Ruston Hartdegen and
associates discovered that a dragon could discriminate among its
permanent keeper, another reptile keeper who had less contact
with the dragon, and a keeper from another animal department.
The dragon was calm with the familiar caretaker, nervous around
the less-familiar reptile keeper, and displayed defensive behav ior
to the keeper from another animal department (R. Hartde gen,
pers. comm.). Kraken, the first dragon hatched at SNZP in 1992,
exhibited the same individualized responses toward familiar and
unfamiliar persons.
London Zoo reptile curator Joan Beauchamp Procter (1928)
examined dragon behavior:
"the question oF the FeroCity oF these liZards is, perhaps,
the Most Misunderstood oF all. all the liZards oF the genus
Fig. 7. Varanus griseus from “Symbolae Physicae-Zoologica” by
Christian Gottfried Ehrenberg in 1828.
Fig. 8. Varanus griseus in John Anderson’s “Zoology of Egypt” in 1898.

Herpetological Review 50(1), 2019
185
varaNus are savage, predatory, and highly strung, and they
use their teeth, Claws and slashing tails with great eFFeCt, as i
have personal Cause to Know. at the Zoo we Consider any large
Monitor More dangerous to deal with than a CroCodile twiCe its
siZe. but, allowing For this, v. koModoeNsis is the gentlest, Most
intelligent, and Most traCtable oF theM all. this is CoMparing
theM with speCiMens only halF their weight oF speCies suCh as
Niloticus, albigularis, beNgaleNsis, salvator, Nebulosus, varius, and
so on. it is quite true that they are very nervous, and also that
they Could no doubt Kill one iF they wished, or give a terrible bite
when taKing Food FroM the hand greedily, but there is no viCe in
theM."
Procter included a photograph of a two-year-old child
standing next to an adult dragon and wrote:
"the dragon, whose naMe is suMbawa, walKed around a very
long table, and without paying attention to the audienCe ate a
large Fowl, several eggs, and a pigeon FroM her hand, allowing
itselF to be sCratChed and patted even when swallowing the Fowl
with enorMous gulps, treatMent whiCh even dogs will not always
perMit … she [at death proved to be a Male] would tear a pig to
pieCes but Can be trusted with Children."
Sumbawa was the host at children’s tea parties a few weeks
after arrival at the Zoo and was perfectly tame with all the guests.
Sumbawa accompanied Procter on strolls through the Zoo
during her inspections investigating everything that might be of
interest. The lizard responded to the voice of its keeper or curator
but disliked having its tympanum touched. Procter’s experiences
and her fondness for Komodo Dragons have recently been
turned into a children’s book, Joan Procter, Dragon Doctor: The
Woman Who Loved Reptiles (Valdez and Sala 2018).
Murphy and Walsh (2006) and Murphy et al. (2002) described
many instances of dragons and humans interacting without
incident. Gordon Burghardt of the University of Tennessee
filmed sequences of a dragon at Zoo Knoxville interacting with
a cardboard box, Frisbee, bucket, small balls, shopping bag
containing a shoe within a cardboard box, and exploratory
tongue-flicking on his torso. The lizard stuck its head into the
bucket and shoe and carried both around the enclosure. At DZ,
a tame adult V. niloticus (Fig. 9) was used in demonstrations for
several years. Atypical for the species, this lizard was completely
tractable and allowed many visitors to pet and hold it.
A most enjoyable read is an account by Eric R. Pianka and
Samuel S. Sweet (2016)—Field Observations by Two American
Varanophiles. For many herpetologists, studying monitor lizards
in Australia would be a dream come true but to actually do so
is very challenging: biting insects, difficult terrain, isolation,
finding and catching lizards in blasting dry heat and dangerous
rainstorms while avoiding injuries from the monitors. ERP spent
about 48 months over a 42-year period in the Great Victoria
Desert. SSS worked 31 months in the field over 13 years in
tropical northern Australia, primarily in Kakadu National Park.
The superb in situ photographs show the beauty and difficulty
in traversing the study sites within the various habitats and the
magnificence of these varanids living there. ERP remembers:
"For one oF My birthdays, helen eMbroidered an aCCurate and
beautiFul varaNus ereMius on the baCK oF a niCe shirt. sadly, i have
grown too Fat and Can no longer Fit into this Fine shirt! when
i was still lean and Mean, i wore it proudly to a herpetologiCal
soCiety Meeting –– as i was walKing along, soMeone behind Me
Called out My naMe –– the guy turned out to be none other than
My good buddy Fellow varanophile jiM Murphy who Knew varaNus
ereMius was My Favorite liZard and who reCogniZed the speCies."
great esCapes
Because of their intelligence and problem-solving abilities,
captive monitor lizards can be quick to exploit defects or flaws in
their exhibits and enclosures or take advantage of keeper errors.
As a result, there are numerous accounts of escapes in zoos; in
some cases it took several days or weeks to apprehend an animal,
and in others, captives were never retrieved. While working at
the Long Island Reptile Museum (LIRM), a former reptile zoo in
New York (see Mendyk 2015), RWM witnessed several monitor
escapes worth noting. A male V. melinus escaped from its exhibit
and worked its way up into the ductwork in the ceiling of a
service corridor where it could not be retrieved. Keepers would
periodically encounter the animal basking out in the open under
overhead skylights in the museum’s gallery when they would
arrive for work in the morning, but it managed to evade recapture
for several weeks. A 1.2-m long V. salvadorii acquired through a
seizure from a local drug dealer’s residence managed to squeeze
through a small gap and access the crawl space in the ceiling
above its exhibit. Perched on ladders with their heads poking up
through the ceiling tiles on opposite ends of the exhibit, RWM and
a fellow keeper attempted to direct the animal towards either side
by poking at it with broomsticks. Poked from the opposite side of
the enclosure, the monitor lunged towards RWM with its mouth
agape, causing him to fall backwards off the ladder and into the
exhibit’s shallow pool below. The resulting sprained ankle was an
acceptable alternative to a bite to the face given the impressive
dentition of the species. RWM was told of an incident involving
an escaped V. cumingi at the LIRM that managed to crawl behind
a wall in the main exhibit gallery. Without hesitation and in front
of numerous museum visitors, the facility’s owner took to the wall
with a sledgehammer, proceeding to punch large, gaping holes
in the drywall until the animal could be located and captured
by hand. Unaware of why this was going on, the looks on the
museum visitors’ faces were priceless (T. Baez, pers. comm.).
Despite varanids’ reputation and propensity for exploiting
weaknesses in enclosures or keeper errors (e.g., leaving an
Fig. 9. Varanus niloticus in John Anderson’s “Zoology of Egypt” in
1898.

Herpetological Review 50(1), 2019
186
enclosure door unlocked), sometimes escaped individuals do
not travel far, or even depart when given the opportunity to
do so. Ruston Hartdegen recalled an incident at DZ where he
transferred an older V. olivaceus to an attached shift enclosure
while the glass window of its exhibit was waiting to be replaced.
The following morning, the curator commented on how great
the V. olivaceus looked on display, having shifted the animal back
into its exhibit the previous night. Knowing that the glass had not
yet been replaced, a perplexed Hartdegen went to check on the
exhibit to find the monitor basking contently on a perch just a
few feet away from the missing window pane of the exhibit!
Some accounts document monitors returning back to the
enclosures they originally escaped from. For example, Kent-
Seville (1897) reported on a V. varius that returned to its outdoor
enclosure 10 days after escaping, but now missing part of its
tail and in poor physical condition. Kent-Seville (1897) also
referenced a monitor (species not identified, but probably V.
salvator) that escaped from its holding enclosure in northern
Borneo that was found back at its enclosure just a few days later.
Grossly underestimating their climbing abilities, keepers at
the Bronx Zoo were surprised when one of two Komodo Dragons
that arrived in 1955 promptly escaped from their enclosure—a
former Galapagos Tortoise exhibit (Dunto 1955; Bridges 1959).
A V. komodoensis nearly escaped from the Antwerp Zoo when
it was taken outside into an uncontained area for photographs
and took off running; luckily a keeper was able to grab its tail
at the last moment before it got away (Berg 1959). Possibly
unsatisfied with the nesting options provided to her, a gravid
female V. salvadorii managed to escape from its enclosure at the
Honolulu Zoo by squeezing through a two-inch gap in the corner
of its exhibit (Meier 2000). When captured and returned to its
enclosure, it immediately returned to the precise spot where it
had escaped from, demonstrating remarkable spatial memory.
Conners (2004) noted that a juvenile V. komodoensis escaped its
outdoor enclosure at Zoo Miami and was free for more than two
months. In his 1958 book, Zoo Hunt in Ceylon, German animal
dealer Heinz Randow described the escape of an enormous 3-m
long V. salvator that had been captured and held at his facility in
Ceylon (now Sri Lanka) awaiting export to a European aquarium.
There, it was housed in a large wooden crate and fed a diet of
flying foxes every other day. One day it managed to escape but
was found shortly thereafter dragging the heavy wooden crate
behind it, to which it had been tethered.
Escapes from private reptile keeper collections are far
more extensively documented in local newspapers, and date
back to the late 1800s (Zandera 1895; Kent-Saville 1897). It is
suspected that escaped or intentionally released pet V. niloticus
are responsible for the introduction and establishment of the
species in southern Florida, USA, where there are now at least
three known populations (Enge et al. 2004; Wood et al. 2016).
Feeding behaviors
Several authors have described that varanid lizards are
capable of modulating their transport kinematics in response to
different prey. Although these lizards use inertial prey transport,
they also modulate tongue and hyoid movements in response to
different prey types. Schaerlaeken et al. (2011) wrote:
"the ability to Modulate Feeding KineMatiCs in response
to prey iteMs with diFFerent FunCtional properties is liKely a
prerequisite For Most organisMs that Feed on a variety oF Food
iteMs. variation in prey properties is expeCted to reveal variation in
Feeding FunCtion and the FunCtional role oF the diFFerent phases
in a transport CyCle. here we desCribe the KineMatiCs oF prey
transport oF two varanid speCies, varaNus Niloticus and varaNus
orNatus."
Smith (1986) described varanid feeding:
"the Morphology and FunCtion oF the tongue and hyoid
apparatus in varaNus were exaMined by anatoMiCal and experiMental
teChniques. MorphologiCal Features unique to varaNus inClude
a highly protrusible tongue that has lost a roughened dorsal
surFaCe, an exCeptionally strong and Mobile hyobranChial
aPParatus, a Well‐deFined Joint betWeen tHe CeratoHyal and
anterior proCess, and a series oF distinCt MusCles inserting at the
anterior hyobranChial region. varaNus is also unusual aMong
liZards in a nuMber oF Feeding behaviors; it ingests prey entirely
by inertial Feeding, as the tongue does not partiCipate in Food
transport."
Thompson (1995) followed the feeding behavior of V. gouldii
in the wild. The abstract from that paper reports:
"two gould’s goannas (varaNus gouldii) were intensively
observed in the seMi-urban environMent oF KarraKatta CeMetery,
perth, western australia. aFter eMerging and basKing to inCrease
their body teMperature, they spent Most oF their tiMe out oF their
burrows Foraging, priMarily in leaves between grave Covers, and
under trees and shrubs. Mean speed oF MoveMent between speCiFiC
Foraging sites was 27.6 M Min-1, whereas the overall Mean speed
while aCtive was only 2.6 M Min-1 beCause oF their slower speeds
while Foraging. a nuMber oF speCiFiC body postures were observed,
inCluding; vigilanCe, walKing, ereCt, and tail swipes. speCiFiC
Feeding and avoidanCe behaviours were also reCorded, along with
the inFluenCe that two speCies oF birds had on their seleCtion oF
Foraging sites."
Large varanids forage in a slow deliberate manner, swinging
the head from side to side and following prey trails by using the
forked tongue to evaluate both sides of the trail without requiring
the lizard to constantly shift from side to side (Schwenk 1994,
2000). Young (1997) reported that monitors lack taste buds. At
DZ, Garrett and Card (1993) found that rapid tongue-flicking
enables monitors to pick up olfactory cues. Losos and Greene
(1988) examined the ecological and evolutionary implications of
diet in monitor lizards. Arboreal monitors have unique ways to
handle prey. Irwin (1994) reported on the behavior and diet of
the Canopy Goanna (V. keithhornei) at the Queensland Reptile
and Fauna Park (now Australia Zoo). Hartdegen et al. (1999)
observed feeding behavior of V. beccarii at DZ. These lizards often
take struggling prey to a horizontal branch used as a permanent
killing station, much like raptors.
Should prey be hidden inside a hole in a tree branch and the
opening too small to accommodate the lizard’s head, a clever
alternative is employed by members of the V. prasinus complex.
Once the prey item is detected by smell or by sight, V. beccarii
and V. prasinus tongue-flicked around the opening to investigate
its content, then stuck their snouts in the opening, only to
discover that the food was out of reach. After the unsuccessful
attempt with their snouts, they reached into the hole with a
forelimb while maintaining eye contact with the food, and the
prey was hooked with the claws. Both species have exceedingly

Herpetological Review 50(1), 2019
187
sharp claws on their forefeet which are inserted into the opening
to impale rodent prey, which is quickly extracted and consumed.
Extraction of food items out of a small opening requires highly
coordinated movements of the forelimb, wrist, and digits (Fig. 10;
see Mendyk and Horn 2011; Mendyk 2012; Kuppert 2013). Shuter
(2014) reported that a 13-yr old captive-bred male V. prasinus
submerged itself underwater to secure prey at the Bronx Zoo.
Hartdegen et al. (2000) described prey laceration by using the
sharp foreclaws of V. prasinus and V. beccarii at DZ.
Traeholt (1993) found that V. salvator dispatches live mice
by seizing them consistently behind the head/cervical region
(76.7%) rather than the stomach (9.0%) or tail (5.0%). [In
contrast, venomous snakes that are ambush predators such as
pitvipers and true vipers carefully strike rodents. If the mouse
or rat approaches frontally, they often wait until the prey offers a
lateral view and strike. Usually the prey is released after the strike,
especially if the rodent is too large and possibly dangerous, and
the snake accurately follows the trail (see Boyer et al. 1996).] He
divided treatment of prey into three broad categoriesō”Shake”,
“Scrape” and “Crush Head and Neck.” Horn (1999) mentioned
teamwork between two V. niloticus as they may cooperate when
raiding bird or crocodile nests. At DZ, an adult V. indicus recently
collected from the wild in West Papua passed shell fragments
from a newly hatched Fly River Turtle (Carettochelys insculpta).
Jaman et al. (2007) evaluated population status and feeding
of V. bengalensis and V. flavescens in Bangladesh (Figs.11, 12). The
study showed that V. bengalensis preferred invertebrates whereas
V. flavescens sought vertebrate prey. The authors concluded
that there was significant niche separation. These differences
suggested that future conservation plans should be aware of
population numbers. Varanus bengalensis are significantly more
numerous than V. flavescens.
Eight V. gouldii hatched at DZ in 1996 were used to compare
chemosensory behavior and prey trail-following (Garrett et al.
1996; Fig. 13). In the trail-following experiment, an S-shaped
trail was laid on a paper substrate and a dead mouse carcass was
pulled along the trail and hidden behind a barrier at the end.
The following variables were recorded: time when the lizards
contacted the trail; time when rodent was located; amount of
time the lizard’s head was within the trail area; total number
of tongue-flicks while in the testing arena; and total number
of tongue-flicks within trail. Naturally, the trails followed lizard
bodies. A series of experiments were performed using these
recently-hatched lizards as a stimulus to study tail-luring in Death
Adders (Acanthophis antarcticus). These lizards were separated
from the snakes with a glass panel and were susceptible to the
lure, lunging at snake tails.
Captive V. albigularis were observed by John (Andy) Phillips
at San Diego Zoo, who found that these lizards are capable of
numerical discrimination (Pianka et al. 2004). The varanids were
fed four snails in an enclosure with separate compartments with
movable partitions—opened one at a time allowing a monitor
to eat each of the four snails. After the last snail was consumed,
the lizard was allowed access into another adjacent chamber
containing four more snails. After the lizard became conditioned
to expect four snails, one snail was removed from some snail
groups—all the test lizards searched extensively for the missing
fourth snail, even when the door to the next group was open.
Fig. 10. Varanus beccarii using the forelimb to probe for inaccessible
prey. From Mendyk and Horn (2011).
Fig. 11. Illustration of Monitor gemmatus (now V. bengalensis) from
“The Animal Kingdom” by Baron Cuvier and P. A. Latreille (Plates,
Vol. II, Reptiles–Fishes) in 1834.

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This clever experiment was expanded to demonstrate that these
monitors can count up to six. If snails were offered in groups of
larger than six, the monitors gave up counting, eating all before
moving on to the next chamber. This ability to count possibly
evolved as a consequence of raiding nests of mammals, birds, and
reptiles, since average clutch or litter size of prey would probably
be less than six. Phillips and associates have extensively studied
varanid biology, publishing their findings in a series of papers
from 1992 to 1998. Varanus albigularis regularly consumes
venomous snakes, including Puff Adder (Bitis arietans), African
Viper (B. caudalis), Egyptian Cobra (Naja haje), and Black-
Necked Spitting Cobra (Naja nigricollis). JBM saw a nature film
of this monitor attacking an adult N. nigricollis. The snake was
grabbed at mid-body and was vigorously shaken and battered
against the rocky substrate, preventing accurate spraying of the
venom. When the snake was disoriented after about 15 min, the
lizard released it and quickly seized the head. The snake was still
moving weakly during swallowing until the end of the episode. It
never was able to bite the lizard during the violent struggle.
One of the most interesting papers on V. albigularis was
written by Bill Branch in 1991 called “The Regenia registers of
Brown (1869–1909). “Memoranda on a species of Monitor or
Varan.” Branch covers all aspects of Alfred ‘Gogga’ Brown’s
extensive observations—sex ratio, size, body proportions,
hemipenial morphology, visceral fat bodies, coloration, diet,
cause of death, longevity, reproduction, gestation period, egg
laying, oviposition, eggs, clutch size, hatchling size, incubation
period, growth, behavior, mating behavior, shedding,
thermoregulation, predation, parasites, exploitation, seasonal
activity, and retreats. The amount of information that Gogga
collected on his captive lizards and on wild counterparts in the
late 19th century is truly astounding.
JBM saw a film at a European monitor conference of an
adult V. dumerilii attacking a large crab (Figs. 14, 15) and it was
grisly. The lizard began by pulling off both pinching claws, then
removing each leg until only the carapace remained. Each part
was quickly ingested. The crab was still alive but finally died when
the monitor crushed it in its jaws and swallowed it piecemeal.
This behavior was discussed by Krebs (1979, 1991, 2016).
Three frugivorous and largely arboreal monitors occur in the
Philippines: Sierra Madre Forest Monitor (Varanus bitatawa),
Mabitang (V. mabitang), and V. olivaceus. Fruits, snails, and
palm nuts are eaten by wild V. olivaceus but four captives at
DZ refused all available fruits, snails, and nuts available from
local Asian markets but fed voraciously on mice and rats.
Invertebrates such as crabs and insects were ignored as well
as birds and bird eggs. Yuyek (2012) described husbandry and
reproduction of V. olivaceus at the Avilon Montalban Zoological
Park; thawed chicken parts and rodents were accepted. Recchio
(2016) outlined husbandry and reproduction at Los Angeles Zoo,
which included a diet comprised of several fruit items. Sweeney
et al. (2017) compared nutritional elements in captive versus
Fig. 12. Varanus flavescens from “Illustrations of Indian Zoology
Chiefly Selected from the Collection of Maj.-Gen. Hardwicke” by
John Edward Gray in 1830–1835.
Fig. 13. Illustration of Monitor gouldii now V. gouldii from “The Liz-
ards of Australia and New Zealand” by John E. Gray and Albert Gün-
ther from 1845 to 1875.
Fig. 14. Varanus dumerilii from “Verhandelingen over de natuurlijke
geschiedenis der Nederlandsche overzeesche bezittingen…” by Sa-
lomon Müller in 1839–44.

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189
wild lizards and found that the sugary cultivated fruits typically
offered in captivity were vastly different nutritionally from the
fruits consumed in nature.
Tourists arrive by ship several times a week to Komodo Island
to watch demonstrations of dragon feeding behavior. A 46-kg
V. komodoensis ate a 41-kg wild pig, which left its belly grossly
distended and dragging on the ground (Auffenberg 1981). JBM
watched dragon feeding behaviors on Rinca and Komodo Islands.
The visitors stood on a high overlook on Komodo Island and the
rangers tossed dead goats down to the dragons. At the former
site, a freshly killed adult goat was presented by the rangers to 20
lizards ranging in size from adult males to subadults. The largest
lizards were near the carcass and the smaller ones dashed in to
grab scraps flung by the bigger ones since cannibalism was a real
danger. The time span between the carcass hitting the ground
and until nary a speck of goat remained was 7 min. Surprisingly,
the lizards did not bite one another. After the feeding, two adult
males engaged in vigorous bipedal combat for ca. 15 min; no
biting took place and the subordinate animal quickly left the
arenaō (see Schuett et al. [2009] for explanation of evolution of
bipedal postures). The rangers tied the hindquarters of a goat to
a tree, so the lizards had to adopt a bipedal stance; they never
jumped to reach the food. The rangers also tied the hindquarter
to a long rope and ran with the lizards following like the pied
piper; fortunately, the humans were faster than the lizards. The
dragons were habituated to the area, waiting for goats to fall from
the sky and no longer showed predatory behavior. The rangers
were worried that the demonstrations led to deleterious effects,
so these shows were discontinued. Quentin Bloxam from Jersey
Wildlife Preservation Trust (pers. comm.) documented that after
the cessation of artificial feeding some of these varanids simply
remained in place and starved to death.
On Rinca, JBM observed a subadult dragon foraging for
over two hours with no success. Every rock or hiding place was
investigated with rapid tongue flicking; the tail was not used to
frighten hidden prey in to the open. A Sambar deer bellowed a
plaintive stress call next to a dirt trail. Ten minutes later, an adult
lizard slowly crossed the trail, presumably tracking the deer,
about 3 m in front of JBM and totally ignored him.
Chris Wemmer told JBM that many years ago, SNZP herp
keepers routinely fed dead animals from the collection after
necropsy to reptiles. Head keeper Lee Schmeltz acquired a
carcass of a Muntjac (known also as the Barking Deer from Asia,
Sri Lanka, Taiwan, Indonesia islands, and central China) that
recently died in the collection and fed it to the V. komodoensis
during visiting hours. The dragon seized the muntjac by the
belly and tossed its head in a violent slashing motion which
eviscerated the deer, splashing the glass front of the enclosure
with blood, metabolic by-products, and entrails. Predictably, the
incident was reported in record time to higher authorities and
Schmeltz was warned never to let it happen again (Murphy and
Xanten 2007, Murphy 2015). Kuppert (2013) recorded trailing
behavior in a dragon at SNZP:
"the sCent trail experiMent Clearly shows this KoModo
dragon’s rtF inCreased greatly as it approaChed the prey and was
in iMMediate proxiMity to it. the experiMent gives insight in how
the trailing behaviour is ManiFested. shorter and More tongue
FliCKs also indiCate intensiFied investigatory behaviour. Knowing
that KoModo dragons have the ability to Follow prey over several
KiloMetres Can be the basis For an olFaCtory-based enriChMent
regiMen. one approaCh Could be to ConstruCt an artiFiCial sCent
trail that leads to a buried Food iteM, siMilar to the one in the
experiMent ConduCted. this approaCh stiMulates the aniMals to be
aCtive. sinCe Many KoModo dragons in Captivity are overweight
(j. gerrits, personal CoMMuniCation 15. Feb. 2012), this Feeding
approaCh Might inCrease an individual’s physiCal exerCise and be a
Mental stiMulus."
deFeCation
For smaller species of monitor lizard and juveniles of larger
taxa, it may be advantageous for an individual not to defecate
close to its refuge site, where pythons and other olfactory-driven
predators could potentially track down their whereabouts. In
captivity, monitors are limited in the distance they can travel
Fig. 15. Hatchling Varanus dumerilii have bright red heads and glossy
black bodies with creamish transverse bands to potentially mimic
several highly venomous sympatric snakes. Illustration by Carel Piet-
er Brest van Kempen (“A Kerangas Forest Floor – Hatchling Dumeril’s
Monitor,” 2012. Acrylic on illustration board, 30” x 20”). Kerangas is
an Iban term referring to the fact that the soil is too poor to grow
rice. Dominant tree species usually belong to the mangosteen family.
Orchids show the greatest species diversity. Species of melastomes,
laurels, myrtles, and gingers are also commonly represented. Many
plant species bear nitrogen-fixing bacterial nodules on their roots,
and carnivorous plants also thrive. Species of the pitcher plant genus
Nepenthes trap insects in leaves that are modified into water-bear-
ing pitchers. Bladderworts (Utricularia spp.) and Sundews (Drosera
spp.) also trap small arthropods.

Herpetological Review 50(1), 2019
190
to defecate, which can pose a problem for dispersing their
feces. With impeccable precision, V. beccarii in RWM’s private
collection learned to aim and direct their feces out a small gap
along the bottom edge of the door to their enclosure, leaving a
mess on the room’s floor daily. Probably serving a similar anti-
predatory function, water monitors belonging to the V. salvator
complex are notorious for defecating in their water in captivity
– leaving keepers with the task of frequently cleaning out water
tubs and pools with some of the most vile and putrid sewage
produced in the herpetological world. Even worse was the keeper
at the LIRM who stumbled while carrying a tub full of rancid V.
salvator water and ended up sloshing it all over himself. Without
a shower at the facility or a change of clothes, he had no other
option but to rough it out for the remainder of the workday in his
soiled clothing. Another keeper sustained a serious bite to the
hand by a V. cumingi while it was submerged in a putrid pool of
fouled water which, in addition to major reconstructive surgery
to the hand, required months of aggressive antibiotic therapy.
Defecation could also be used to confuse predators. At
the Bronx Zoo, a female Ornate Monitor (V. ornatus) regularly
defecated on top of her freshly nested clutches of eggs (Lee
2000)—possibly as a scent deterrent to egg predation. A female V.
salvadorii at the Denver Zoo defecated exclusively on top of her
nest site for a period of more than three months (Trout, 2007).
Similar behaviors have also been observed in several other
monitor species in captivity (RWM, unpubl. data; F. Retes, pers.
comm.).
enriChMent and training
Hayes et al. (1981) called for zoo workers and others working
with captive animals to include amphibians and reptiles in their
enrichment schemes, countering a common belief that they
possessed limited cognitive and emotional needs. Behaviorist
Gordon Burghardt has researched environmental enrichment
and cognitive complexity in reptiles, including varanids,
focusing on implications for captive populations (Burghardt
1977, 2013). In White-throated Monitors (V. a. albigularis), a
large carnivorous species, Burghardt and associates found that
sensory cues and foraging decisions were influenced by various
snail presentations (Kaufman et al. 1996). In his many papers on
improper environmental effects and deleterious end results in
captive reptiles, he outlines ways to make the complex lives of
varanids and other reptiles far more interesting (see Burghardt et
al. 2002 for unexpected behavioral elements in V. komodoensis).
Monitors have shown remarkable learning abilities. As an
example, 16 Black-throated Monitors (V. albigularis microstictus)
reared from hatching at the Dallas Zoo in off-exhibit housing
were used in trials to track differences in learning between lizards
in complex, enriched settings and others in stark enclosures as
described in Manrod (2003) and Manrod et al. (2008):
"a transparent Food tube Contained several prey. the Food
tube allowed the Monitors to obtain prey by using hinged doors at
either end oF the tube to aCCess Food. all eight liZards learned to
open the tube, insert head, and Capture the prey within 10 Min."
Not surprisingly, varanids in complex environments learned
more quickly.
A prey density-dependent foraging experiment by Kaufman
et al. (1996) is described in the paper’s abstract:
"results showed that at high prey density, these liZards
seleCted large over sMall snails. at low prey densities, however,
large and sMall snails were seleCted at an equal rate. apparently,
when prey densities are high, the liZards have the opportunity to
seleCt the larger prey iteMs without inCurring loCoMotor Costs.
these data support optiMal Foraging theory but are unique in that
they are an exaMple FroM a little-studied, widely Foraging speCies
oF liZard."
Using several taxa of varanids at Zoo Atlanta (V. komodoensis,
V. griseus, V. rudicollis, V. albigularis), Diaan Gaalema ran multiple
experiments for food choice, reinforcer preference, and visual
discrimination. The results show that these types of trials can be
undertaken in a zoo.
Firth et al. (2003) examined responses by V. ornatus, V.
albigularis, and the Savannah Monitor (V. exanthematicus) to a
repeated food source, asking if this was evidence for association
learning.
"Food loCation tiMes have been reCorded in three Captive
Monitor liZards (varaNus spp.). the results, in the ForM oF
regression equations, showed that in general the tiMe taKen to
loCate the Food deCreased with the nuMber oF tiMes the Food was
oFFered."
Hellmuth et al. (2012) provided suggestions for operant
conditioning and training, using V. niloticus, V. beccarii, and V.
komodoensis in examples of trained behaviors for facilitating
veterinary procedures in reptile species in zoos. Murphy and
Walsh (2006) discussed various examples of training in V.
komodoensis:
"at the london and houston Zoos, ultrasonography without
anesthesia is used to deterMine sex and assess reproduCtive
Condition on dragons; the dragons reMain CalM during the
proCedure.
in london, a large Male dragon (naMed raja) was trained to
use a restraint box For target training. dragons are trained to
assoCiate a target on a stiCK with a Food reward. the target is Moved
into and out oF the restraint Crate so that the dragons beCoMe
CoMFortable entering this restriCted spaCe, whiCh FaCilitates
Moving theM. this interesting exaMple oF operant Conditioning
used Food as the initial Cue — then the reward FrequenCy was
gradually reduCed, using a CliCKer (sound produCing deviCe) as
a bridge between the target and reward (r. gibson, pers. CoMM.).
at the pittsburgh Zoo, a study was initiated to test a dragon’s
spatial MeMory by exaMining whether dragons use proxiMal (near-
by) or distal (Far away) visual Cues to reMeMber the loCation oF
a Food reward hidden in the liZard’s exhibit. preliMinary results
support the hypothesis that a dragon used proxiMal Cues to
reMeMber the loCation oF the Food and additional experiMents
are underway to deterMine iF a dragon Can use distal Cues in other
CirCuMstanCes (h. ellerbroCK, pers. CoMM.)."
Several zoos have focused on conditioning large varanids
for voluntary participation in routine veterinary procedures
including radiographs (Anonymous 2006; Ainsworth 2013),
nail trimmings (Herndon 2001; Ainsworth 2013), weight
measurements (Herndon 2001; Anonymous 2006), blood
(Anonymous 2006; Camina et al. 2013) and saliva collection
(Gully 2013), and crate training for transport (Mader and Divers
2003; Helmuth et al. 2012) or medical procedures (Fleming and

Herpetological Review 50(1), 2019
191
Skurski 2013). At Taronga Zoo, Boylan (2011) recalled training a V.
komodoensis to walk through the zoo to its new enclosure, and
Donato (2008) mentioned training a large V. salvadorii at the Saint
Augustine Alligator Farm for use in educational demonstrations.
“liZard Kings”
In 2009, the US Public Broadcasting System (PBS) presented
an award-wining film on varanids in the series NOVA called
“Lizard Kings,” created by Gisela Kaufmann and Carten Orlt.
Segments included history, hatching, a Perentie attacking and
consuming a highly venomous Eastern Brown Snake (Pseudonaja
textilis), reactions to wildfires, and interactions with humans.
A number of research projects and observations by
prominent biologists are presented. Lizard Man Eric Pianka
discusses his long-term lizard diversity studies in the Red Sands,
Great Victoria Desert in Australia with field assistant Stephen
Goodyear. The film shows views of his field camp, use of pit
traps, trailing by following tail marks left in sand, construction
of daily nocturnal burrows by V. gouldii for thermoregulation,
and tracking using Lizardcam with Oxford biologists Lucas Bluff
and Christian Rutz. Eric’s sense of humor is in full bloom—his
personal contest called “flies out of my face” where he swats
at the unbelievable density of these annoying creatures and is
quite pleased with himself when he kills two with one stroke.
Imagine his unbounded pleasure if three or more are smashed!
Two nightmares follow—a giant monitor chasing and swallowing
him and “War Crimes,” a Nuremberg-like trial explaining the
thousands of lizards (35,000+) killed for his studies with a V.
giganteus as judge and many lizards (thorny devils, frilled lizards,
bearded dragons and so on) as jury: Verdict—death by hanging!
Pianka has watched lizard diversity negatively impacted by
climate change over the past several decades in Australia. Due
to a ca. 20% increase in rainfall, spinifex and other desert plants
have been replaced by shrubs and other moisture-loving flora,
causing a dramatic shrinkage in saurian biodiversity.
Gordon Burghardt and associated researchers demonstrate
target training experiments with V. exanthematicus at the
University of Tennessee. Former Curator Ian Stephens at London
Zoo shows an array of different human-dragon interactions such
as trailing, targeting, and allowing keepers to brush off dead skin
with soapy water on the entire body of the famous dragon, Raja.
Michael Cota and others show an amazing sequence of
V. salvator combatting, mating, and foraging for table scraps
between and around the diners’ feet/legs and on top of the
tables at Dusit Zoo, Thailand.
Fig. 16. This superb volume incorporates virtually all
information on varanid lizards. Thirty-five of the most
prominent authors studying monitor biology provide up-
to-date overviews on all taxa. The volume also includes
information on the varanoid clade—helodermatids, and
the taxon Lanthanotus borneensis. The species Estesia
mongoliensis is known exclusively from fossils.
Fig. 17. Illustration of Odatria punctata, now V. tristis from “The Liz-
ards of Australia and New Zealand” by John E. Gray and Albert Gün-
ther from 1845 to 1875.
Fig. 18. Illustration of Varanus caudolineatus from “Catalogue of the
Lizards of the British Museum, Volume III” by George A. Boulenger
in 1887.

Herpetological Review 50(1), 2019
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general
Ziegler et al. (2016) compiled data on zoo varanid holdings:
to gain an overview oF Monitor liZards held in Zoos, inCluding
the speCies and nuMbers oF individuals Kept and the nuMber oF
Keeping institutions, we analyZed ColleCtion inForMation FroM the
ZoologiCal inForMation ManageMent systeM (ZiMs) database.
our analysis perForMed in MarCh 2016 revealed that there are
50 speCies oF Monitor liZard Kept globally in 308 Zoos, with 39
oF these speCies Kept in a total oF 131 european Zoos. eleven
globally-Kept speCies were laCKing in european Zoo holdings, and
nine speCies were Found exClusively in european Zoos. oF the 79
Currently reCogniZed speCies oF Monitor liZard, 30 (38 %) are not
Currently held in Zoos. although ZiMs data are Certainly not
CoMplete, there is a disCernible trend that only a Few speCies are
widely Kept by the Zoo CoMMunity; whereas Most speCies are poorly
represented or not represented at all.
A fantastic book on varanids was published by Pianka et
al. (2004; Fig. 16). Murphy (1971, 1972) provided data on Indo-
Australian varanids at DZ and a list of captive monitors in the
collection between 1966 and 1993 (Figs. 17, 18). Winston Card
published a paper with Arnold Kluge on hemipenial morphology
and systematics in 1995. Christie (1982) successfully introduced
three incompatible male V. varius at the Indianapolis Zoo.
Murphy et al. (2002) investigated factors necessary for
the medical and captive management and conservation
of V. komodoensis. At SNZP, Gray et al. (1966) discovered
amoebiasis and Spelman et al. (1996) described anesthesia
in V. komodoensis. Hyde et al. (2016) found the oral and skin
microbiomes of captive dragons are significantly shared with
their habitat. Parasite burdens of captive varanids were reported
by Bosch (1999).
Köhler (1992) assessed disease in monitors maintained in
European collections, and Mendyk et al. (2013) studied mortality
in captive varanids at the Bronx Zoo over a 40+ year period.
Mendyk (2015) also assessed life expectancy and longevity in
seven species of zoo-maintained varanids.
RWM and associates have published a number of varanid
papers listed in the references section. He is also the founding
editor of the open-access, peer-reviewed online journal Biawak,
which is devoted exclusively to monitor biology and husbandry.
Some wild monitor lizards occasionally find zoos to be
suitable homes. A study by Karunarathna et al. (2008) was
conducted on the grounds of the National Zoological Gardens
(NZG) in Sri Lanka. Varanus salvator and V. bengalensis (protected
in Sri Lanka) live on zoo grounds. Varanus salvator was the first
Fig. 19. Arrow shows 2-m Varanus salvator swimming at Lumpini
Park, Bangkok with city skyline in the background.
PHOTO BY R. W. MENDYK
Fig. 20. Varanus salvator is abundant on the grounds and in the wa-
terways of Bangkok’s Dusit Zoo. The monitors can even be seen inside
various zoo exhibits including those of large carnivores such as tigers.
PHOTO BY R. W. MENDYK

Herpetological Review 50(1), 2019
193
reptile in Sri Lanka to receive legal protection in 1937 (as well
as in the 1992 CITES appendix II list), while V. bengalensis has
been placed in CITES appendix I (De Silva 1996). It is clear that
the NZG is an important suburban refuge for threatened fauna
in the wet zone of Sri Lanka. During the survey period, several
threats within the NZG were observed, including water pollution
and the excessive use of chemicals.
Varanus salvator can be found living in urban environments
of many Southeast Asian cities. In Bangkok, Thailand, monitors
exceeding 2 m in length roam freely in Lumpini Park, amidst
the backdrop of a bustling megacity with towering skyscrapers
surrounding the park (Fig. 19). Varanus salvator is also abundant
on the grounds and in the waterways of Bangkok’s Dusit Zoo (see
Cota 2011a,b). Here, because of their high population density,
conspicuousness, and indifference to human activity, many
aspects of the species’ biology can be observed easily during a
single visit, including ritualized combat, courtship, copulation,
and predation on fish and turtles. The monitors here are so
abundant that they can even be seen inside various zoo exhibits,
including those of large carnivores such as tigers (Fig. 20). At
Singapore Zoo, staff must regularly watch out for wild V. salvator
and Reticulated Pythons (Malayopython reticulatus) as they
pose a serious threat to collection birds and small mammals (S.
Lafebre, pers. comm.).
There are many contrary views of whether Komodo Dragons
are venomous. Fry et al. (2009) published a provocative paper:
"our MultidisCiplinary analyses paint a portrait oF a CoMplex
and sophistiCated tooth/venoM CoMbined-arsenal Killing
apparatus in v. koModoeNsis and its extinCt Close relative v.
priscus. thus, despite a relatively weaK sKull and low bite ForCe,
we suggest that the CoMbination oF highly and very speCiFiCally
optiMiZed Cranial and dental arChiteCture, together with a
CapaCity to deliver a range oF powerFul toxins, MiniMiZes prey
ContaCt tiMe and allows this versatile predator to aCCess a wide
range oF prey inCluding large taxa. these results indiCate that v.
priscus was the largest venoMous aniMal to have ever lived."
However, other researchers urged caution in accepting the
hypothesis that dragons are venomous until additional evidence
is forthcoming (Weinstein et al. 2012; Weinstein et al. 2013;
Sweet 2016). Ballard and Antonio (2001) reported on two bites
sustained by zoo keepers from V. griseus that caused symptoms
suggestive of toxicity including dysphagia. Whether it could
be considered venom, there does appear to be some active
anticoagulatory properties of the saliva that accompanies the
bites of at least some species of monitor lizard. Don Gillespie and
associates have published on blood and salivary composition
(Montgomery et al. 2002; Gillespie et al. 2000; Gillespie et al.
1997). There was a V. komodoensis bite at Los Angeles Zoo
sustained by a journalist that required reconstructive surgery of
the foot and ankle; this report also included a case history of a
bite to a zookeeper (Ducey et al. 2016). RWM recalls a colleague
receiving a very minor, superficial bite from an adult female V.
melinus which caused excessive bleeding that took nearly an
hour to clot. A surprising amount of bleeding relative to the size
of the bite and considerable localized pain was also experienced
from the bite of a male V. beccarii (RWM, pers. obs.). At SNZP, a
juvenile V. prasinus bit the finger of a keeper, causing the hand to
swell (LA, pers. obs.).
seMinal booK on husbandry and Captive ManageMent
This section is based on a German work, Tasks and Problems
of Zoo Biology in Studying the Life Manifestations of Lower
Amniotic Animals (Reptiles), which Hans-Günter Petzold from
Tierpark Berlin published in 1984. This compendium, which
incorporates terriarum and scientific literature, was completed a
few days before his premature death on 19 November 1982. This
English translation, Lives of Captive Reptiles, was published by
SSAR in 2008.
"until the Middle oF the 20th Century nothing was Known
about the inCubation tiMes oF Monitor eggs. in his great Monitor
Monograph Mertens (1942) was able only to express the assuMption
that the eggs oF varaNus Niloticus lay For about 10 Months in
terMite hills until they hatCh. despite the FaCt that these are
well-Known and popular “show” aniMals in large terraria, no
breedings had oCCurred up to that tiMe in Captivity. however,
the eggs oF varaNus koModo eNsis had already been desCribed in
1932 by brongersMa (up to 11.5 CM long!). in the batavia (today
djaKarta) Zoo the speCies was said to have reproduCed in an
outdoor enClosure in 1941/42 (aCCording to Mertens, 1952,
without Further details); dathe [personal CoMMuniCation]
doubts this as the result oF his own later investigation), in the
jogjaKarta Zoo, on the other hand, breeding was suCCessFul in
1968 (busono, 1974). — in Zoos and in isolated Cases involving
expert terrariuM praCtitioners the breeding oF representatives
oF these large sauria has been suCCessFul only sinCe 1962. the
Known inCubation periods oF the eggs vary between a Mere 92 days
(varaNus gilleNi, CF. horn, 1978) and 139 days (v. tiMoreNsis in
the basle Zoo, rüegg, 1973) in the sMaller speCies over 170–177
Fig. 21. Robert Mertens (1894–1975) was a pioneer in the
study of varanid lizards. He was the curator at Senckenberg
Museum in Frankfurt am Main, Germany.
PHOTO COURTESY OF KRAIG ADLER

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194
days (v. exaNtHeMaticus albigularis in the san diego Zoo, staedeli,
1962) up to 327 days (v. salvator, variation range 241–327 days
under identiCal inCubation Conditions, KratZer, 1973 a; 9 Months
in the san antonio, texas Zoo at 28.9°C, bowers, 1981). — up
until now we Know oF suCCessFul breedings with Corresponding
data oF nine Monitor ForMs."
"pellet ForMation in reptiles is not ConFined to CroCodiles.
hediger (1934) was First to Call attention to genuine pellet
ForMation in reptiles at hand oF [FroM] varaNus iNdicus whiCh
voMited pellets aFter Feeding with MiCe, reMinisCent in siZe and
CoMposition oF those ForMed by the tawny owl: “they Contained
parts oF sKeletons and Matted hair.” it was possible to undertaKe
More thorough experiMents in the berlin tierparK with varaNus
salvator (petZold, 1967 b). Monitor pellets are less CoMpaCt
and Constant in shape than CroCodile pellets, More “rag-liKe”;
also, the nuMeriCal relations are diFFerent (9 MiCe Fed to a
dwarF CroCodile yielded approxiMately 100 individual pellets; in
Monitors only about a tenth as MuCh). the digestive Capability
oF the Monitor stoMaCh exCeeds that oF the owl stoMaCh (only
oCCasionally teeth and bone parts were Found, no sKulls) but
does not equal that oF the CroCodile and diurnal bird stoMaCh.
in the stoMaCh oF a varaNus koModoeNsis whiCh had Fasted For
Four Months aFter its CatCh, Mertens (1942) still Found bones oF
a young indian saMbar."
"as regards squaMate reptiles, until now pellets Consisting oF
MaMMalian reMains are Known exClusively aMong Monitors, while
aCCording to observations Made in Zoos, pellets CoMposed oF bird
Feathers, Claws and beaKs are also expelled by giant snaKes (liasis
fuscus: FroesCh, 1966; pytHoN Molurus bivittatus: lederer, 1942
b). here, too, we are undoubtedly dealing with “genuine” pellets.
lederer (l. C.) also Found bird pellets in varaNus koModoeNsis; the
Feather quills were “aCtually pasted together.” My own atteMpts
to Feed varaNus salvator with ChiCKen and guinea Fowl ChiCKs
yielded Feathers brought up in the water basin, “but it Could
not be deterMined whether during the digestion oF birds in the
stoMaCh oF the Monitor pellets was even ForMed, or whether the
Feather pellet was only so loosely balled up that — in Contrast
to the hair pellets — it instantly dissolved in water aFter being
voMited up; the latter is More liKely” (petZold, 1967 b)."
"this CoMpilation, ending iNter alia [aMong other things]
with the partiCularly beautiFul suCCess oF breeding the eMerald
Monitor, inCludes only the initial breedings. while at this tiMe
we Cannot as yet speaK oF “Conservation breeding” oF Monitors—
not all the oFFspring grew up—we Can nevertheless note with
satisFaCtion that international Cooperative eFForts to build up
breeding groups serve this objeCtive (basel - san diego 1976
Fig. 22. Illustration of Le Varan à deux bandes (Varanus bivittatus,
now V. salvator) in Alfred E. Brehm’ s “Les Merveilles de la Nature. Les
Reptiliens et les Batraciens” in 1885.
Fig. 24. Varanus indicus from “Histoire naturelle, générale et particu-
lière, des reptiles…” by F. M. Daudin, an X-XI [1802–1803].
Fig. 23. Illustrations in “Locupletissimi rerum naturalium thesauri”
by Albertus Seba in 1734–1765. The lizard pictured may be a Nile
Monitor (V. niloticus or ornatus). Many of the varanid illustrations
appearing in Seba’s first two volumes of Thesauri were copied by
other artists and included in subsequent publications (Shaw, 1802;
Goldsmith, 1840). The two species most often pictured by Seba were
Varanus niloticus and V. salvator. Seba’s Thesauri is considered to be
the most comprehensive survey of biodiversity of the 18th century,
and today ranks among the most valuable and sought after illus-
trated works on natural history, commanding prices of nearly US
$500,000 (Aaron Bauer, pers. comm.).

Herpetological Review 50(1), 2019
195
with varaNus koModoeNsis, CF. anonyMous, 1976 b). the total
inventory oF KoModo Monitors in Zoos aMounted in 1980 to
20 aniMals (with an estiMated voluMe oF populations in nature
oF 6,000, aMong tHeM, HoWeVer, only about 400 ‐‐♀♀ Capable oF
reproduCtion)."
"until the Middle oF the 20th Century the inCubation tiMes
oF Monitor eggs (CF. the data under 3.1.10) were praCtiCally
unKnown. in the MeantiMe, the piCture has Changed; at least 9
speCies reproduCed in Captivity — in part repeatedly, but to our
Knowledge not yet ever in the 2nd generation (CF. visser, 1975;
busono, 1974; internat. Zoo yearb., vol. 1–20)."
"CoMMendably the nuMerous published reports oF Keeping
and breeding oF the last two deCades did not liMit the dates
oF nutritional studies, ClutChes and inCubation, although the
latter altogether were new (CF. 3.1.10.). the partly extreMe
long inCubation tiMes required More CoMparative studies. in
the san diego Zoo the sex deterMination oF KoModo Monitors
was aCCoM plished through quantitative MeasureMent oF the
steroid horMones in the blood; also, the First Karyo graM oF this
speCies was Made (with at First not yet Fully proven indiCation oF
heterogaMy oF the ♀♀; benirsCh Ke & KuMaMoto, 1981) and along
with that, additional Material was ColleCted toward Knowledge
oF the ChroMosoMe evolution in the genus varaNus (CF. King &
King, 1975, as well as seCtion 3.1.1.). egg MeasureMents and egg
weights as well as growth rates and developMent oF the oFFspring
oF several Monitor speCies in various Zoos were reCorded 124. in
addition, Zoos were able to MaKe observations oF the ritual CoMbat
behavior oF the ♂♂ in the FunCtional systeM oF reproduCtion and
about the (For now, only suspeCted) biannual egg-laying oF the
CoMMon water Monitor as well as the digestive-physiologiCal
phenoMenon oF pellet ForMation in Monitors (CF. seCtions 3.1.5.
as well as 3.2.1.)."
"in the san diego Zoo the sex deterMination oF KoModo
Monitors was aCCoM plished through quantitative MeasureMent oF
the steroid horMones in the blood; also, the First Karyo graM oF this
speCies was Made (with at First not yet Fully proven indiCation oF
heterogaMy oF the ♀♀; benirsCh Ke & KuMaMoto, 1981) and along
with that, additional Material was ColleCted toward Knowledge
oF the ChroMosoMe evolution in the genus varaNus (CF. King &
King, 1975, as well as seCtion 3.1.1.). egg MeasureMents and egg
weights as well as growth rates and developMent oF the oFFspring
oF several Monitor speCies in various Zoos were reCorded]. in
addition, Zoos were able to MaKe observations oF the ritual CoMbat
behavior oF the ♂♂ in the FunCtional systeM oF reproduCtion and
about the (For now, only suspeCted) biannual egg-laying oF the
CoMMon water Monitor as well as the digestive-physiologiCal
phenoMenon oF pellet ForMation in Monitors (CF. seCtions 3.1.5.
as well as 3.2.1.).”
the Future
Prominent lizard ecologist Eric Pianka (2012) summarized the
state of the planet and constructed a pretty depressing picture,
especially for future naturalists. Developers, environmental
pirates and exploiters, tycoons, and others who view the natural
world as something to be only used for human needs and
pleasures will have a much easier time getting by as manmade
objects continue to litter the world. Those persons who treasure
the natural world will be selected against in a true Darwinian
fashion.
"in the end, the question May not be so MuCh why did i write
this little booK [tHe lizard MaN speaks 1994], but rather why
did you read it? i long For a siMpler existenCe. i despise standing in
lines or waiting For traFFiC lights to Change. objeCts and noises
oF huMan origin are obnoxious to Me. i hate being FenCed in,
unable even to get oFF the road. i Cannot tolerate the thought
oF a world in whiCh i Can’t get to pristine wilderness, let alone
a world without any wilderness at all. ( we seeM to be alMost
iMpervious to, and unaware oF, Changes oCCurring around us,
perhaps beCause they oCCur on a tiMe sCale oF deCades, too slow
to be perCeived. but iF one Could travel FroM the 1960’s to the
1990’s, the response Might be More liKe “hey, wait a Minute!”
unFortunately, MuCh oF the younger generation doesn’t even
Know what they’ve lost and are losing.) we don’t iMprove on
nature as we landsCape and pave over the surFaCe oF the planet. i
thinK buildings, FenCes and roads are ugly. i Keep CoMing baCK to
the outbaCK in yet another Futile atteMpt to esCape FroM Creations
oF huMan origin, Crowding, overpopulation, and regiMentation.
My ex-wiFe helen used to say that i was born a Century too late.
perhaps we all were. perhaps you read this in your own atteMpt to
esCape FroM urbaniZation."
Pianka continued:
"people soMetiMes asK Me why i study liZards. or worse, soMe
say “what good are liZards?” to whiCh i respond with “what good
are you?” those who would thinK, let alone asK, suCh a narrow-
Minded question seeM to Me to be hopelessly anthropoCentriC.
liZards are speCtaCular and beautiFul Fellow earthlings that
Fig. 25. Illustration of Varanus gilleni and V. eremius. From Baldwin
Spencer (ed.). 1896. “Report on the work of the Horn Scientific
Expedition to Central Australia. Part 2: Zoology.” These pygmy
monitors (subgenus Odatria) have often been featured in scientific
publications.

Herpetological Review 50(1), 2019
196
deserve our Full respeCt and Care. they were here long beFore us
and deserve to exist on this spaCeship, too."
"sadly, “wildliFe ManageMent” is soMewhat oF a FarCe:
Currently we are Failing to adequately Conserve speCies or
habitats—we huMans do not even have the will to liMit our
own population! huMans have now draMatiCally altered the
eCology oF over halF oF the land surFaCe oF this our one and
only spaCeship planet earth. Conservation biology is a Man-Made
eMergenCy disCipline rather liKe surgery is to physiology or war
is in politiCal sCienCe. wild aniMals Could and would Flourish
iF people Could Manage to share the planet and leave theM large
enough undisturbed areas oF habitat. however, even iF we Could
soMehow designate and Maintain large nature reserves, the
MenaCe oF irreversible global warMing seeMs destined to taKe a
heavy toll on all earthlings. hopeFully, with new approaChes
and inCreased global eFForts, liZards, inCluding varanids, will
be aMong the survivors oF this Current Massive anthropogeniC
extinCtion event."
Acknowledgments.—This contribution is dedicated to Robert
Mertens (1894–1975), a pioneer in the study of varanid lizards (Figs.
21–25). He was the curator at Senckenberg Museum in Frankfurt am
Main, Germany. The late Walter Auffenberg at University of Florida
in Gainesville (no slouch when it came to studying dragons) was
contacted by Mertens as he was planning his first trip to the United
States and asked if Auffenberg would take him on collecting trips
throughout Florida. Auffenberg quickly agreed and so off they went.
Mertens knew the scientific names of every herp, bird, mammal,
invertebrate, tree, plant, and so on. Walt was amazed so he asked
Mertens how he knew all of the fauna and flora since he had never
been to the US. Mertens said that he had memorized all relevant
dichotomous keys beforehand in Germany—truly an astounding
memory. His experiences throughout his trip are detailed in his
book Zwischen Atlantik und Pazifik (1951). He kept large living
collections at the museum and his home, leading to the classic Die
Warn- und Droh-Reaketionen der Reptilien (1946). One interesting
paper concerned V. salvadorii at Wilhelma Zoo (1960). Visitors tried
to challenge him to identify an obscure herp; it was said that he never
missed! He published a monograph on the Varanidae in 1942, which
included 20 plates of many specimens and skulls. on 5 August 1975,
he was bitten by an African rear-fanged twig snake (Thelotornis) and
died 18 days later. In his diary, he wrote “a singularly appropriate end
for a herpetologist.”
For acquisition of specimens at DZ, we thank Walter Auffenberg,
Chris Banks (Melbourne Zoo), Sir Edward Hallstrom (Sydney
Zoo), Heini Hediger (Zürich Zoo), Arnold Kluge, Dale Marcellini
(Smithsonian National Zoological Park), and Ken McCloud (US Fish
& Wildlife Service).
We thank Kraig Adler, Tony Baez, Daniel Bennett, Judith Block,
Carel Pieter Brest van Kempen, Gordon Burghardt, Michael Cota,
Robert Hansen, Ruston Hartdegen, Lucien Heichler, David Kirshner,
Ken McCloud, Joseph Mendelson III, Matt Neff, Eric Pianka, Jessica
Amanda Salmonson, and Samuel Sweet for various courtesies. Many
of the scans were from the collections at Smithsonian Institution
Natural History Museum library and Ernst Mayr library at Harvard
University by librarians Polly Lasker and Dana Fisher, respectively.
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