South American Journal of Herpetology, 1(1), 2006, 42-53
© 2006 Brazilian Society of Herpetology
KERATOPHAGY IN REPTILES: REVIEW, HYPOTHESES, AND
JOSEPH C. MITCHELL1,4, JOHN D. GROVES2, AND SUSAN C. WALLS3
1 Department of Biology, University of Richmond, Richmond, Virginia 23173 USA. E-mail:
2 North Carolina Zoological Park, 4401 Zoo Parkway, Asheboro, North Carolina 27205 USA.
3 U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, Louisiana 70506 USA.
4 Corresponding autor.
ABSTRACT: Consumption of the whole or part of a reptile’s own shed skin or that of a conspecific (keratophagy) has been documented
in 248 species of lizards in 16 families and 19 snakes in four families. There are no authentic cases in turtles or crocodilians. An
earlier review based primarily on zoo records noted keratophagy in 160 species of lizards, of which 16 were from literature sources
designating field observations or stomach contents. We added an additional 16 captive observations for lizards and brought the
total to 89 species for which this behavior has been documented in nature. Eating shed skins of conspecifics has been observed in
23 lizard species in five families. All of the 19 snake species known to have eaten their shed skins, except one, a Clelia clelia,
were in captivity. We reviewed six hypotheses that may explain the occurrence and evolution of keratophagy. These are the
Nutritional Hypothesis, Skin sensitivity hypothesis, Artificial Behavior Hypothesis in Snakes, Accidental Hypothesis, Predator
Avoidance Hypothesis, and the Reduced Parasite Load Hypothesis. The Nutritional and Artificial hypotheses provide the least
explanatory power for this behavior. The remaining four hypotheses have varying levels of predictability but each may function
within different contexts. We provide recommendations for elucidation of these hypotheses in our discussions of them. Finally, our
attempts at electronic searches were hindered because of the variation in the terminology used for this behavior, and because most
authors did not include an appropriate term in their list of keywords or in the abstract. We recommend standardization of the term
“keratophagy,” and that authors of diet and behavioral studies in which consumption of shed skin was observed include this term
in abstracts and key words.
KEY WORDS: behavior, keratophagy, lizards, snakes, turtles, predator avoidance, reptiles, shed skin.
The consumption of shed skin has been observed in
a broad taxonomic diversity of reptiles. It was first noted
in Anolis carolinensis by Lockwood (1876) and Monks
(1881). Although it is especially well known in geckos
(M. A. Smith, 1935; Bustard and Maderson, 1965;
Weldon et al., 1993), it also occurs in other lizard
groups and in some snakes (Groves and Groves, 1972).
Literature references refer to this behavior as the con-
sumption of an individual’s own shed epidermis and
occasionally as consumption of shed skin of one indi-
vidual by a conspecific. The terminology for this be-
havior, however, has not been consistent. Groves and
Groves (1972) introduced keratophagy, whereas other
terms were used by Iverson (1979), Weldon et al.
(1993), and Seipp and Henkel (2000).
Bustard and Maderson (1965) provided the first
review of keratophagy in 17 lizard species and Wel-
don et al. (1993) extended the taxonomic coverage from
observations provided by a large number of zoos and
reached a total of 153 species. Mattlin (1946) was the
first to describe a snake eating its own skin. Groves
(1964) and Groves and Groves (1972) published oc-
currences in an additional four species. Kuch (1998)
brought the total to eight. We expand the review of
this behavior in reptiles and add additional informa-
tion that allows generation of hypotheses. Unless oth-
erwise noted, our review includes observations of in-
dividuals eating their own shed skin. In cases where
Mitchell, J. C., et al. 43
the information available indicates only that the be-
havior was recorded, we use the terms “captivity” and
“field” to specify the environmental conditions in which
it occurred. We present our information in three ways.
(1) We list new, simple observations of keratophagy in
captivity to add to the list in Weldon et al. (1993) for
lizards and those in Groves and Groves (1972) and
Kuch (1998) for snakes. (2) We include all literature
available to us in which observations of this behavior
were documented in the field whether published previ-
ously or not. This includes notes of “shed skin” in ta-
bles on a species’ diet diversity. (3) We provide details
of observations noted in the literature on consumption
of shed skin from a conspecific by another individual.
Higher order taxonomy follows Zug et al. (2001) and
Han et al. (2004). Our aim in this paper is to provide
an updated review of species performing this behav-
ior, examine new and published hypotheses on its caus-
es and benefits, and suggest recommendations for test-
ing these hypotheses.
Hydrosaurus amboinensis – Lederer (1929) observed
captives eating the shed skin of conspecifics.
Physignathus cocincinus – Captivity (J.B. Murphy,
Sitana ponticeriana – Sharma (2002) found shed skins
in several stomachs, although it is not clear if they
were their own skins or those of others.
Uromastyx acanthinura – Captivity (R.E. Honegger,
Celestus agasepsoides – Shed skins were found in the
stomachs of 41 field-caught specimens (White et al.,
Elgaria coeruleus – Fitch (1935) found tail skin in a
Ophisaurus ventralis – Shed skin was found in the stom-
ach of a field-collected specimen (Palmer and
Wetmorena haitiana – Two of 22 wild-caught individ-
uals contained shed skin (Cizek et al., 1990).
Chamaeleo namaqueisis – Captivity (Burrage, 1973).
Nephrurus levis – Captivity (Wagner and Lazik, 1996).
Gerrhosaurus flavigularis – Shed skins were found in
field-collected specimens (Loveridge, 1936, 1942).
Zonosaurus madagascariensis – Captivity (J.B. Mur-
phy, pers. comm.).
Aeluroscalobotes felinus – Captivity (J. B. Murphy,
Coleonyx variegatus – captivity (Cope, 1900; J.D.
Groves, per. obs.). Klauber (1945) observed cap-
tive geckos detach and eat their own slough and that
of conspecifics. Parker and Pianka (1974) recorded
four of 185 wild-caught specimens with shed skin
in their stomachs. They regularly eat their sloughs,
if not always (J.D. Groves, pers. obs.).
Diplodactylus (Strophurus) elderi – Bustard and Mad-
erson (1965) observed juveniles eating their shed
skin in the wild.
Oedura marmorata – Bustard and Maderson (1965)
observed juveniles eat shed skin in the wild.
Oedura monilis – Shed skin was found in stomach con-
tents of a field-collected specimen (Bustard and
Oedura tryoni – Bustard and Maderson (1965) ob-
served juveniles eat shed skin in the wild.
Rhacodactylus auriculatus – Four of 19 field-caught
specimens had shed skin in their stomachs (Bauer
and Sadlier, 1994). Seipp and Henkel (2000) noted
that Rhacodactylus spp. usually swallow their shed
skins completely, even freshly-hatched young.
Afrogecko porphyreus – Bustard and Maderson (1965)
observed juveniles eat shed skin in the wild.
Bavayia sauvagii – Shed skin was found in 8 of 8 field-
caught specimens (Bauer and DeVaney, 1987).
Chondrodactylus angulifer – One of four specimens
collected in the field contained shed skin (Bauer
et al., 1989).
44 Keratophagy in reptiles
Christinus marmoratus – Bustard and Maderson (1965)
observed juveniles eat shed skin in the wild.
Gehyra australis – Large portions of shed skin have
been found in wild caught specimens (Bustard and
Gehyra variegata – Large portions of shed skin have
been found in wild caught specimens (Bustard and
Gonatodes humeralis – Vitt et al. (1997a) found shed
skin in stomach contents of field-collected speci-
mens. Shed skin was found in 4 of 124 field collect-
ed lizards (Miranda and Andrade, 2003).
Gymnodactylus geckoides – Shed skin was found in
10 of 370 wild lizards (Colli et al., 2003).
Hemidactylus frenatus – Taylor (1963) observed a ne-
onate consume its first shed skin in the field.
Auffenberg (1980) noted that gecko skin was often
found in their stomachs.
Hemidactylus haitianus – Noble and Bradley (1933)
reported that captive adults and hatchlings were ob-
served eating shed skin of conspecifics.
Hemidactylus turcicus – Three shed skins were found
in 167 field collected specimens (Saenz, 1996).
Homopholis wahlbergii – Captivity (D.G. Broadley,
Nactus pelagicus – Shed skin was noted in the stom-
ach of a single field-caught specimen (Bauer and
Nactus serpeninsula – Vinson (1975) recorded that one
of eight wild-caught adults contained an entire shed
Pachydactylus geitje – Bustard and Maderson (1965)
observed juveniles eat shed skin in the wild.
Ptenopus garrulus – Shed skin was found in 2.6% of
640 wild caught specimens (Hibbitts et al., 2005).
Tarentola annularis – Loveridge (1947) noted that cap-
tives carefully peeled shed skin off their limbs like a
glove and ate it.
Tarentola mauritanica – Gil et al. (1994) found shed
skins in stomach contents of field-collected specimens.
Teratoscincus scincus – Captivity (J.B. Murphy, pers.
Thecadactylus rapicauda – Shed skin was noted in
stomach contents of field-collected specimens (Vitt
and Zani, 1997).
Amblyrhynchus cristatus – On several islands in the
Galapagos, J.D. Groves observed skin passed in
feces and ingestion of lizard’s own skin, mostly from
the legs and dorsum and lateral surfaces of the body.
Anolis amouri – Shed skin was found in 5 field-col-
lected lizards (Lenert et al., 1994).
Anolis carolinensis – Hamilton and Pollack (1961)
noted that two of six field-collected anoles contained
parts of their own shed skin. Lockwood (1876) and
Monks (1881) described keratophagy in captive
specimens. Greenburg (1978) provided a photograph
of social grooming in which one lizard is eating the
shed skin of another.
Anolis chrysolepis – Vitt and Zani (1996) noted shed
skin in stomach contents in field-collected specimens.
Anolis cristatellus – Captivity (Spieler, 1946). Shed
skin is common in stomachs of field-collected spec-
imens (Wolcott, 1924; Fitch et al., 1989).
Anolis equestris – Captivity (Petzold, 1982). Four of
five wild individuals contained shed skin (Herrel and
Anolis garmani – One of 31 wild specimens examined
by Herrel and O’Reilly (2006) contained shed skin.
Anolis longitibialis – Five of five field-collected indi-
viduals contained shed skin (Gifford et al., 2002).
Anolis porcatus – Meshaka et al. (1997) found shed skin
in stomach contents of a field-collected specimen.
Anolis limifrons – Field observation only (R. Andrews,
pers. comm. to J. D. Groves).
Anolis nebulosus – Jenssen (1970) observed removal
and ingestion of shed skin by anoles in natural pop-
Anolis nitens – Shed skin was found in one of 184 wild-
caught specimens (Vitt et al., 2001).
Anolis oxylophus – One lizard contained a complete
skin, presumably his own (Vitt et al., 1997b).
Anolis recordii – Captivity (Petzold, 1982).
Anolis roquet – Wingate (1965) recorded one speci-
men of 30 with its shed skin or that of a conspecific
in its stomach.
Anolis sagrei – Field observation (Losos and de
Anolis trachyderma – Shed skin was found in nine of
180 wild-caught specimens (Vitt et al., 2002).
Callisaurus draconoides – H.M. Smith (1946) noted
shed skin in a presumably field-collected specimen.
Pianka and Parker (1972) found shed skin in 13 of
469 wild-caught specimens.
Cophosaurus texanus – Durtsche et al. (1997) found
shed skin in stomach contents of a field-collected
Mitchell, J. C., et al. 45
Ctenosaura similis – Captivity (J.B. Murphy, pers.
Cyclura carinata – Iverson (1979) recorded that 12 of
54 individuals had skin fragments in their stomachs
and that a female contained a male’s dorsal spine.
Cyclura cychlura – Murphy (1969) observed captives
pull shed skin from conspecifics and then eat it.
Enyalius bilineatus – One of two wild-caught speci-
mens examined by Vanzolini (1972) contained its
own shed skin.
Enyalius brasiliensis – One of 14 wild-caught lizards
contained shed skin (Van Sluys et al., 2004), and
one of 89 contained had shed skin in its stomach
(Teixeira et al., 2005).
Enyalius leechii – Shed skin was found in stomach con-
tents of field-collected specimens (Vitt et al., 1996).
Holbrookia propinqua – Judd (1976) found shed skin
in one of 101 specimens.
Leiocephalus barahonensis – Shed skin was found in
five field-collected lizards (Micco et al., 1997).
Phrynosoma cornutum – Shed lizard skin was noted in
the stomach of one of 10 field collected specimens
(Lemos-Espinal et al., 2004).
Phrynosoma modestum – Shed skin was noted in the
stomach of one of 12 field collected individuals (Le-
mos-Espinal et al., 2004).
Phrynosoma platyrhinos – Pianka and Parker (1975)
noted that shed skin was found in field collected
specimens from throughout its range.
Polychrus acutirostris – One field-collected specimen
contained its own shed skin (Vitt and Lachner, 1981).
Sceloporus undulatus – One of 60 field-collected fence
lizards contained shed skin in its stomach (Hamil-
ton and Pollack, 1961).
Tropidurus hispidus – One of 23 wild caught speci-
mens contained shed skin (Van Sluys et al., 2004).
Tropidurus montanus – Two of 32 wild caught speci-
mens contained shed skin (Van Sluys et al., 2004).
Uma notata – Carpenter (1963) observed captive indi-
viduals eating their own shed skin and that of con-
Uma paraphygas – Gadsden and Palacious-Orona
(1997) found shed skin in stomach contents in one
of 19 field-collected specimens.
Uma scoparia – Carpenter (1963) observed captive
individuals eating their own shed skin and that of
Urosaurus graciosus – Vitt and Ohmart (1975) found
shed skin in one of 87 field-collected lizards.
Heliobolus lugubris – Shed skin was noted in 5 of 45
field-caught specimens (Castanzo and Bauer, 1998).
Lacerta agilis – Gvozdik (1997) found shed skin in a
Pedioplanis lineoocellata – Shed skin was found in
one of 43 field-caught specimens (Castanzo and
Pedioplanis namaquensis – Castanzo and Bauer (1998)
found shed skin in two of 71 field-caught specimens.
Caledoniscincus austrocaledonicus – Shed skin was
found in 3 of 3 field-caught specimens (Bauer and
Ctenotus grandis – Twigg et al. (1996) found shed skin
in four stomachs of field-collected specimens (Twigg
et al., 1996).
Egernia coventryi – Clemann et al. (2004) found shed
skin in 26% of 47 wild caught specimens.
Egernia striolata – Bustard (1970) found that four of
35 wild-caught specimens contained shed skin in-
cluding shed skin from their feet.
Eumeces fasciatus – Fitch (1954) found 23 instances
of skink slough in an analysis of 738 food items.
McCauley (1939) noted that a half-grown skink had
some of its own scales in its stomach. Field (De-
Graff and Rudis, 1983)
Eumeces inexpectatus – Hamilton and Pollack (1961)
found two of 31 field-collected lizards with shed
skin in their stomachs.
Glaphyromorphus emigrans – Skink scales were found
in the stomach of one field-caught specimen (Auffen-
Leiolopisma telfarii – Vinson (1975) found pieces of
shed skin in the feces of six wild specimens.
Mabuya agilis – Rocha et al. (2002) found shed skin
in the stomach of a wild-caught specimen.
Mabuya bistriata – Vitt and Blackburn (1991) noted
the presence of shed skin in field-collected speci-
Mabuya frenata – Two of 239 field-collected lizards
had shed skin in their stomachs (Vrcibradic and
Niveoscinsus ocellatus – Shed skin was found in stom-
achs of field-collected specimens (Wapstra and
Scincella lateralis – Hamilton and Pollack (1961) not-
ed that one of 142 lizards had eaten shed slough.
46 Keratophagy in reptiles
Brooks (1964) found that 1% of 327 field-collected
specimens contained shed skin.
Sigaloseps deplanchei – Bauer and DeVaney (1987)
found shed skin in a single field-caught specimen.
Trachylepis acutilabris – Castanzo and Bauer (1993,
1998) found tail fragments and shed skin in 3 of
146 in field-caught specimens.
Trachylepis binotata – Three of 40 field-caught liz-
ards contained shed skin (Castanzo and Bauer,
Trachylepis quinquetaeniata – D.G. Broadley (pers.
comm.) found shed skin in the stomachs of field-
Trachylepis sulcata – Shed skin was found in 10 of 58
field-caught specimens (Castanzo and Bauer, 1998).
Crocodilurus amazonicus – Captivity (R.E. Honegger,
Dracaena guianensis – Captivity (R.E. Honegger, pers.
Varanus niloticus – Captivity (R.E. Honegger, pers.
Xantusia henshawi – Brattstrom (1952) found four
wild-caught specimens with shed skins in their stom-
Xantusia riversiana – Brattstrom (1952) recorded
17 wild-caught specimens from throughout the
range with shed skin in their stomachs and Fellers
and Drost (1991) found shed skin in 47 of 268
fecal samples and in one of 26 flushed food bo-
luses in wild-caught specimens from Santa Bar-
Apodora papuana – Captive observation by O’Shea
and Bigilae (1991).
Python molurus – Shipkowski (1980) observed a cap-
tive male eat pieces of its own shed skin.
Thamnophis sirtalis – Captive observation by Hall-
Bitis nasicornis – A captive-born juvenile ate a portion
of its shed skin (Russell, 1999).
The phenomenon of an individual consuming its
own shed skin or that of a conspecific has been called
keratophagy (Groves and Groves, 1972), epidermoph-
agy (Iverson, 1979), dermatophagy (Weldon et al.,
1993), and ceratophagia (Seipp and Henkel, 2000).
The use of these various terms, together with a general
lack of adequate information in titles, abstracts and
key words of articles, has made it difficult to conduct
electronic literature searches on this topic. For instance,
a recent computer search (using the Institute for Sci-
entific Information [ISI] Web of Knowledge) on the
terms “keratophagy” and “dermatophagy,” revealed
very different results. Only one citation (Kuch, 1998)
was common to both searches. Similarly, a pertinent
review by Weldon et al. (1993) was only revealed by a
search on “dermatophagy.” Searches on more inclu-
sive phrases, such as “reptiles and diet” or “shed skin
in diet” were too vague and either provided mostly ir-
relevant results or none at all. Use of “reptiles and diet
and shed skin” only produced one result, a paper by
Vitt et al. (2002) which was not included in the results
of any of the other searches. We therefore suggest that
one common term, keratophagy, be used in reference
to an individual with shed skin in its diet. Moreover,
abstracts and key words (if applicable) should include
this term and phrases with this terminology to maxi-
mize the chances of an electronic literature search tag-
ging a given citation.
Some authors have obscured the occurrence of
keratophagy in species under study. For example, Pi-
anka (1969, 1986 Appendix E) incorporated lizard
sloughed skin in his “lizard and sloughed skin” and
“all vertebrate material” categories, respectively, for
desert lizards on three continents. It is difficult, if not
impossible, to discern which species of the seven in
western North America, 19 in the Kalahari Desert of
Africa, and 32 in the Australian deserts had eaten their
shed skin. Instances of shed skin in reptile diets war-
rant more detailed attention than it has received previ-
ously. Listing number of individuals with observation
details would help future reviewers of keratophagy in
reptiles better understand the significance of this be-
Mitchell, J. C., et al. 47
Bustard and Maderson (1965) listed 17 species of
lizards that had eaten shed skins, of which four were
under natural conditions. Petzold (1982) listed keratoph-
agy in nine genera of geckos, three genera (and two
species) of iguanids, and one genus of skink known at
that time. Weldon et al. (1993) listed 144 species in
which keratophagy had been observed in captivity and
16 from literature sources that had occurred in nature.
They included two species (Oedura marmorata,
O. tryoni) listed by Bustard and Maderson (1965) that
did not exhibit keratophagy and did not include one
that did (O. monilis). We include the corrections in this
review. Our list expands the total lizard species known
to exhibit keratophagy in captivity to 159 and those in
which it has been documented in the field to 89. Un-
doubtedly, these totals are likely below actual numbers
due to the problems with searching the literature on
this topic and because many authors have not included
specific information on consumption of shed skin in
Keratophagy is now known to occur in 16 of the 21
families of lizards recognized by Zug et al. (2001) and
Hans et al. (2004). Of these, Gekkonidae and Iguanidae
contain the majority of known instances, 68 and 79,
respectively. Twenty-four species of skinks, 18 species
of agamids, and ten or fewer species in the remaining
families have been documented to exhibit keratophagy.
Weldon et al. (1993) suggested that most geckos eat
their shed skin, however, Bustard and Maderson (1965)
noted that at least three species they studied did not.
Keratophagy is commonly practiced in some species.
Anolis carolinensis (Iguanidae) performs this behav-
ior on a regular basis (Bustard and Maderson, 1965).
Both juvenile and adult Eublepharis macularius
(Gekkonidae) eat their entire sheds regularly, if not al-
ways. Of 287 observations in captivity, 98% consumed
their shed skins (J.D. Groves, pers. obs.). Why do some
species eat their skin regularly and others rarely, if at
all? This aspect of lizard behavior is obviously under-
Nineteen snake species have been observed to con-
sume their own shed skin; all but one of the reported
cases of keratophagy are based on captive animals. The
only natural observation is of a Clelia clelia in Guiana
(Beebe, 1946). This behavior is now reported to occur,
in addition to the four species noted above, in Ahaetul-
la ahaetulla, Alsophis elegans, Bitis arietans, Boiga
blandingii, Bungarus fasciatus, Bungarus multicinc-
tus, Clelia clelia, Coluber constrictor, Lampropeltis
getula, Lampropeltis triangulum, Naja melanoleucus,
Notechis scutatus, Python sebae, Thamnophis sirtal-
is, and Uromacer oxyrhynchus (Beebe, 1946; Mattlin,
1946; Groves, 1964; Groves and Groves, 1972; Ke-
own, 1973; Groves and Altimari, 1977; Petzold, 1982,
1983; Haagner, 1991; Weldon et al., 1993; Hallmen,
1998; Kuch, 1998; J.B. Murphy, pers. comm.). Klaub-
er (1956) noted that a few snakes are known to eat
their shed skins, presumably from his observations at
the San Diego Zoo, but that it does not occur in rattle-
snakes. The stimuli for inducing this behavior in cap-
tivity are unknown but the result may be an artifact of
In a sample of 36 Trachemys scripta, Parmenter
(1980) found shed epidermal scutes in the stomachs of
seven. Parmenter and Avery (1990) mentioned turtle
scutes, pebbles, sand and wood in the diet of this spe-
cies, suggesting that turtle scutes may be ingested while
foraging on the bottom of aquatic habitats. This view
is consistent with the foraging behavior of this species
reported by Moll and Legler (1971). Thus, keratoph-
agy may not be the correct interpretation of this occur-
rence. The only other record known to us, Chelodina
longicollis, was a captive reported to us by J.B. Mur-
phy (pers. comm.). Consumption of the relatively large
scutes may not occur frequently, although researchers
should pay attention to stomach contents and feces to
ascertain its relative occurrence. Epidermal scutes of
these reptiles may be secondarily ingested while per-
forming other behaviors, such as grooming algae (Reilly,
1973; Meshaka, 1988) or foraging at the bottom of
Neill (1971) mentioned that scales of their own or
of conspecifics are sometimes found in alligator (Alli-
gator mississippiensis) stomachs. We do not believe,
however, that crocodilians exhibit keratophagy. Their
skin and shedding practices do not suggest this behav-
ior because scales are shed continuously as small flakes
and large plates (Zug et al., 2001). The occurrence of
scutes reported by Neill may have been cannibalism, a
behavior known for crocodilians (Polis and Myers,
1985; Mitchell, 1986).
Of particular interest in our review are the instanc-
es of one individual eating the shed skin of a conspecif-
ic. Weldon et al. (1993) listed occurrences in 16 spe-
cies in four families of lizards (Agamidae, Gekkonidae,
Iguanidae, Scincidae) and none in snakes. We noted its
occurrence in one agamid (Hydrosaurus amboinensis),
two geckos (Coleonyx veriagatus, Hemidactylus hai-
48 Keratophagy in reptiles
tianus), and four iguanids (Anolis carolinensis,
A. roquet, Cyclura cychlura, Uma notata). All instanc-
es were observed in captivity, although the U. notata
were in a large field enclosure (Carpenter, 1963). Do
lizards perform social grooming? What is the purpose
of this behavior and under what circumstances does it
occur? Additional, detailed observations of this behav-
ior should be published to help build a database for
Several hypotheses have been proposed to explain
the occurrence of keratophagy in reptiles. We review
these views, add two additional hypotheses, and note
which ones are amenable to experimental testing.
Taylor (1963) first hypothesized that consumption
of neonatal shed skin was the first meal of a neonate
lizard, implying that some nutritional value was ob-
tained from it. Bustard and Maderson (1965) explored
the possibility that shed skin was a source of vitamin D
that had been produced by the action of sunlight in ver-
tebrate skin. They rejected the hypothesis on the grounds
that the many recorded observations of slough eating
by nocturnal geckos were counter to the presumed cor-
relation of basking with keratophagy. They also sug-
gested that sloughs may be a source of protein. How-
ever, to our knowledge, little is known regarding the
nutritional and energetic composition of squamate shed
skin. Such an analysis would enhance our understand-
ing of whether keratophagy may be nutritionally ad-
The nutritional requirements of the 19 snakes noted
above were presumably assumed to be filled by the prey
provided in captivity. It is not possible to determine
whether the physiological state of the snake was defi-
cient in a compound that they may have found in their
shed skins. The lack of literature records on keratoph-
agy in snakes weakens the application of the nutrition-
al hypothesis to this group.
Skin sensitivity hypothesis
Some lizards may find the drying slough on their
skin irritating and the process of removing it with their
mouths triggers an ingestion response. The skin of gec-
kos may be more sensitive than other lizard groups,
hence the widespread occurrence of keratophagy in this
family. Loveridge (1947) stated that “T [arentola].
A. annularis assists the moulting of its extremities by
seizing a flake of scarf skin in its jaws and, while hold-
ing its claws curled, slowly draws off the slough as if it
were a glove. So slowly and carefully is this done that
it would seem that the reptile was sensitive about its
removal.” The skin sensitivity hypothesis seems inap-
propriate for snakes because the slough had not been
removed from the snake’s body before consumption in
any of the 19 cases noted above.
Artificial Behavior Hypothesis in Snakes
Groves and Groves (1972) concluded that keratoph-
agy in snakes was artificial and possibly influenced by
the reptile-eating tendency of these species. Of the 19
species noted above, all but three, Bitis arietans, Py-
thon molurus, and Thamnophis sirtalis are known to
include reptiles in their diet. All cases involved captive
individuals and, as far as we are aware, none of the
snakes repeated the behavior. Although numerous
snakes have exhibited cannibalism (Polis and Myers,
1985; Mitchell, 1986), none of those reports or other
studies of snake diets (e.g., Uhler et al., 1939; Fitch,
1949, 1999; Ernst and Ernst, 2003) indicated that shed
skin had been found in stomachs of wild-caught ani-
mals. Thus, the circumstantial evidence supports the
artificial behavior hypothesis.
Keratophagy may occur because pieces of the skin
become entangled in the reptile’s teeth and the best
means of removal is ingestion (Bustard and Maderson,
1965). These authors’ initial observations, those of
Weldon et al. (1993), and our review of additional spe-
cies and the literature do not support this hypothesis.
Predator Avoidance Hypothesis
Because predatory snakes and lizards use integu-
mentary-derived, olfactory cues to track their prey (e.g.,
Weldon and Schell, 1984; Mullin et al., 2004),
keratophagy may be a means by which reptilian prey
minimize or eliminate some of the cues to which their
predators respond. Some lizards, particularly the eu-
blepharine geckos, regularly eat their entire skins. At
least some of these lizards (e.g., Coleonyx variegatus,
Eublepharis macularius and Hemitheconyx caudicinc-
tus) also deposit their feces in areas away from their
Mitchell, J. C., et al. 49
colonies. In captivity, these communal defecatoriums
are generally as far away from the rocks or other cover
in their enclosures (J.D.Groves, pers. obs.). It is possi-
ble that keratophagy in these lizards may serve an anti-
predator behavior. By placing slough skins in their fe-
ces (J.D. Groves, pers. obs.) and depositing this mate-
rial as far away as is possible from where they spend
the day, they may deter predatory snakes from finding
their locations. Additional work being conducted by one
of us (JDG) may shed some light on the relationship.
Some lizards of the Family Agamidae are also known
to exhibit feces displacement (Pianka and Pianka, 1970).
The North American skink Eumeces laticeps can de-
tect chemical odors from sympatric predator snakes and
discriminate these chemical stimuli from similar ones
derived from a sympatric snake that does not eat liz-
ards (Cooper, 1990). Dial (1990) showed that Coleo-
nyx variegatus can also distinguish chemically between
predator and non-predatory snakes. Of these lizards,
only C. variegatus, is known to exhibit keratophagy,
Cannibalism can occur in captive snakes if prey odors
are detected on a conspecific (Mitchell, 1986). Perhaps
keratophagy occurred in some of the 19 snakes above
because the shed skin contained prey odors that stimu-
lated prey consumption behavior. Snake skin chemicals
serve to stimulate feeding behavior in some species (Wel-
don and Schell, 1984). They are also detected by liz-
ards, salamanders, and mice so that these potential prey
may avoid predation (Madison et al., 1999; Shapley,
2003; Punzo, 2005). We hypothesize that, in some cas-
es, keratophagy may be triggered by chemical cues con-
tained in the shed skin of prospective prey and may there-
fore be a prelude to a predatory event. If this hypothesis
is accurate, one would predict that keratophagy would
be more frequent in ophiophagic and saurophagic snake
predators, including those that engage in cannibalism
(Polis and Myers, 1985; Mitchell, 1986).
Reduced Parasite Load Hypothesis
Reptiles are commonly infested with a variety of ec-
toparasites, including mites and ticks in terrestrial liz-
ards and snakes (e.g., Chaivabutr and Lawan, 2002;
Ameh, 2005). Some reptiles have specialized adapta-
tions that reduce ectoparasite loads. For instance, some
species of marine turtles have cleaning symbioses with
fishes that remove ectoparasites (Losey et al., 1994; S.
H. Smith, 1988). Moreover, many species of lizards have
evolved “mite pockets,” which typically house damag-
ing chigger mites and presumably limit damage caused
by ectoparasites (Arnold, 1986; Bertrand and David,
2004; Salvador et al., 1999; but see Bauer et al., 1990).
The shedding of skin in reptiles, along with the
molting of feathers in birds and of hair in mammals,
may be a more generalized means of reducing infesta-
tions of ectoparasites (Moyer et al., 2002 and refer-
ences therein). A logical extension of this hypothesis
for reptiles is that consumption of the shed skin perma-
nently removes ectoparasites from an individual’s hab-
itat, thus minimizing the potential for reinfestation. To
our knowledge, there have been no experimental tests
of whether skin shedding reduces ectoparasite loads in
reptiles. We know of no studies of whether keratoph-
agy minimizes reinfestation of individuals from eggs,
larvae and adult ectoparasites contained within shed
skins. One prediction of this hypothesis is that indi-
viduals with heavier ectoparasite loads should engage
in keratophagy more than individuals with lighter loads.
Experimentally increasing the ectoparasite load of test
individuals and monitoring their keratophagous behav-
ior relative to control individuals could test this predic-
tion. We assume that the parasites are shed with the
skin. Although this may be true in some instances, trom-
biculid mite larvae have their stylets embedded in the
dermis and typically are not shed with the skin (A.M.
Bauer, pers. comm.). Their bodies might be ripped off
from the heads if the shed is pulled appropriately. Thus,
extreme care must be taken to ascertain the numbers
that are removed and those that remain in whole or in
Summary and Conclusions
The results of our review of keratophagy in reptiles
suggest that there may be ecological, nutritional, sur-
vival, and evolutionary fitness benefits to this behav-
ior, at least for lizards. A more complete understanding
of this behavior awaits additional reports and experi-
mental testing of the hypotheses we noted above. Fu-
ture reports of keratophagy should include a descrip-
tion of the environment in which the reptile performed
the behavior, age, size, and sex of the individuals, a
complete description of the behavior, and insofar as
possible, the individual’s nutritional status and prey
consumption history. Publication of additional obser-
vations in the field and in captivity using standardized
terminology is clearly warranted.
50 Keratophagy in reptiles
We are grateful to the librarians of the University of Rich-
mond, Smithsonian Institution, University of Tennessee, Vir-
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Research Center in Lafayette, Louisiana for assistance with lit-
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versity of Richmond were particularly helpful over the years
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observations and literature were contributed by A.M. Bauer, R.
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