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ARTHROPOD/HOST INTERACTION,IMMUNITY
Interactions Between the Chilean Recluse Spider
(Araneae: Sicariidae) and an Araneophagic Spitting Spider
(Araneae: Scytodidae)
MAURICIO CANALS,
1,2,3
NICOLA
´S ARRIAGADA,
4
AND RIGOBERTO SOLI
´S
4
J. Med. Entomol. 1–8 (2015); DOI: 10.1093/jme/tju021
ABSTRACT In Chile, all necrotic arachnidism is attributed to the Chilean recluse spider, Loxosceles
laeta Nicolet, a species that shares the microenvironmental habitats with the spitting spider Scytodes
globula Nicolet. The latter species has been proposed as a potential predator of L. laeta. For this re-
search, we studied the interaction between both species during individual encounters to assess the possi-
bility of population regulation of L. laeta cohorts exposed to this potential predator. We found that in
most encounters S. globula prevailed. Also, S. globula preys on spiderlings of L. laeta, with a population
effect on cohorts of this species. These findings suggest that S. globula may be influencing L. laeta
populations in central Chile. The population regulation of L. laeta by predation would be important
because this species, in the absence of predators, has a high reproductive rate, and it can maintain
populations of large size. However according to our results, although S. globula may aid in the reduction
of both spiderling and adult L. laeta populations, and perhaps other Loxosceles species, it is insufficient
for biological control of Loxosceles species. Its presence together with other control measures such as
hygiene of the rooms can help to decrease loxoscelism incidence.
KEY WORDS Loxosceles laeta,Scytodes globula, spider predation, loxoscelism
Introduction
Loxoscelism is a health problem caused by the bite of
spiders of the genus Loxosceles (Araneae: Sicariidae).
The cases in Chile are attributed to Loxosceles laeta
(Nicolet), Loxosceles gaucho Gertsch in Argentina,
Loxosceles intermedia Mello-Leita˜o in Brazil,
Loxosceles reclusa Gertsch and Mulaik in the United
States, and Loxosceles rufescens (Dufour) in Mediterra-
nean areas (Gertsch 1967,Gertsch and Ennik 1983,
Reyes et al. 1991,Vett er 2 008).
In Chile, all necrotic arachnidism is attributed to the
Chilean recluse spider, L. laeta, a species that may be
preyed upon by the spitting spider Scytodes globula
Nicolet (Araneae: Scytodidae). The biology of these
two species is not well known (Fernandez et al. 2002;
Canals et al. 2004,2008;Canals and Solı´s 2013,2014;
Tau care -Rı´os et al. 2013).
L. laeta is a solitary spider of domestic habitats, found
within households usually in dark corners, cracks, closets,
clothing, and bath towels, but sometimes can be found
outdoors. Its activity is preferentially nocturnal; high tem-
peratures are a factor that favors its development (Sche-
none and Letonja 1975;Schenone 1998,2003,2004;
Schenone et al. 2001). With respect to diet, in Chile it
has been reported that this spider feeds on flies, moths,
and other small arthropods (LeviandSpielman1964;
Schenone et al. 1970,1989,2001;Schenone 1998,2003,
2004;Parra et al. 2002). From the medical point of view,
the epidemiology of loxoscelism incidents coincides with
nocturnal activity. Epidemiology also suggests larger spi-
der populations and greater activity during the summer
(Schenone 1998,2003,2004;Schenone et al. 2001).
A potential predator of L. laeta in Chile is the solitary
species, S. globula, a member of a group of spiders
known as spitting spiders with recognized araneophagic
habits (GilbertandRayor1985,Bowden 1991). The
Scytodes spiders feed on spiders and insects such as
Diptera, Lepidoptera, and Mantodea, avoiding schlero-
tized and aggressive prey (Fernandez et al. 2002).
During predation these spiders spit an adhesive
substance through their chelicerae, immobilizing their
prey (Foelix 1996,Araujo et al. 2008). These spiders are
active during twilight and night and their thermal pref-
erences and desiccation tolerances are similar to those
of L. laeta (Alfaro et al. 2013,Canals et al. 2013).
S. globula is distributed in South America in Chile,
1
Programa de Salud Ambiental, Instituto de Salud Poblacional,
Escuela de Salud Pu´ blica Salvador Allende G., Santiago, Chile.
2
Departamento de Medicina, Facultad de Medicina, Universidad de
Chile, Santiago, Chile. CP: 8380413 and Departamento de Zoologı´a;
Facultad de Ciencias Naturales y Oceanogra´ficas, Universidad de
Concepcio´ n, Concepcio´ n, Chile.
3
Corresponding author, e-mail: mcanals@uchile.cl.
4
Departamento de Ciencias Biolo´ gicas Animales, Facultad de Cien-
cias Veterinarias y Pecuarias, Universidad de Chile, Santiago, CP:
8820808 Chile.
V
CThe Author 2015. Published by Oxford University Press on behalf of the Entomological Society of America.
For Permissions, please e-mail: journals.permissions@oup.com
Journal of Medical Entomology Advance Access published February 2, 2015
Bolivia, Argentina, Brazil, and Uruguay. Like L. laeta,
this species is common in human dwellings and gardens
of houses of central Chile (Fernandez et al. 2002).
While there are references that suggest predation on
L. laeta by S. globula, there are few studies that support
this (Fernandez et al. 2002,Canals and Solı´s 2013).
For example, Ramires (1999) and Ades and Ramı´res
(2002) documented the results of encounters between
S. globula and three species of Loxosceles:L. laeta,
L. gaucho,andL. intermedia. These authors reported
that within 30 min of introduction, virtually all L. laeta
were alive, although they were victims of the adhesive
substance and wrapped in silk lines. Of the 22 preda-
tion events recorded, on three occasions the defense of
L. laeta caused leg autotomy in S. globula and, in two
instances, it was L. laeta which preyed on S. globula.
Knowing that the activity rhythms, thermal prefer-
ences, and tolerance to desiccation of these species are
similar, it is necessary to describe the direct interaction
that occurs when these species meet (Hertz et al. 1993,
Angilletta et al. 2002). If an encounter between L. laeta
and S. globula is produced, we need to know the out-
come of the interaction between these species both at
the individual level (predatory acts) and population
level (ability to regulate the population) in order to de-
termine if S. globula can be an effective biological con-
trol agent (Wiedenmann 2000).
In this study, we analyzed the interaction between
S. globula and L. laeta during individual meetings and
the possibility of population regulation of cohorts of
L. laeta exposed to this potential predator, with the fol-
lowing working hypotheses: 1) as there is some experi-
mental evidence that suggests predation of L. laeta by
S. globula, we propose that the most common response
in individual meetings of the two species will be the
death of L. laeta; 2) as there is some experimental evi-
dence that suggests predation of L. laeta by S. globula,
we propose that this species has the potential to regu-
late populations of L. laeta.
Materials and Methods
Individual Interactions. Forty sexually differenti-
ated individuals of L. laeta and S. globula were col-
lected inside institutional storehouses and inside
human dwellings in the cities Santiago and Valparaiso
in Chile between December 2012 and December
2013. Sexual differentiation can be recognized from 5th
and from 6th moult in S. globula and L. laeta, respec-
tively (Galiano 1967,Fernandez et al. 2002,Canals and
Solı´s 2014). The spiders were maintained individually
in 750-ml plastic bottles, from the reception of the indi-
viduals to the beginning of the experimental trials.
All individuals were maintained with a photoperiod
of 12:12 (L:D) h, at 20 62C, near the preferred tem-
perature of both species (Alfaro et al. 2013) in the labo-
ratory of Ecology and Behavior of Faculty of Veterinary
Sciences at the University of Chile. The temperature
was monitored with a maximum–minimum thermome-
ter. Prior to the initiation of experimental encounters,
spiders were transferred to an incubator with inverted
L:D cycle, where they were maintained for at least 7d.
This allowed experimental trials to be conducted dur-
ing the day, but in the scotophase of the spiders.
Thirty-two interspecific encounters were performed in
sealed circular plastic containers (diameter 19.5 cm;
depth 7 cm). The encounters were recorded with a high
resolution digital video camera (SONY HDR-CX 700,
Chicago, USA), with night shot, in WAV format. The
rivals in each encounter were randomly chosen. They
were sexed, and their body mass was measured with an
analytic balance Shimadzu (AUX 220, Japan; 61mg).
The capture and the manipulation of individuals were
performed by using brushes, anatomic tweezers, and
rubber gloves, avoiding direct contact with the spiders.
First, the resident spider was introduced in the
experimental arena and was maintained for 1 wk
for habituation before the encounter. Thirty-two
individuals of L. laeta (66.21 690.30 mg) and 32 indi-
viduals of S. globula (76.33623.87 mg), with a body
mass ratio R ¼mass of S. globula /massof
L. laeta ¼0.607 60.448, were used in the encounters.
Sixteen individuals of L. laeta (Ll) were male
(m
b
¼105.21 648.75 mg) and 16 female (m
b
¼
238.82 666.14 mg), and 18 individu als of S. globula
(Sg) were male (m
b
¼71.17 621.68 mg) and 14 female
(m
b
¼82.80 624.76mg). The encounters were distrib-
uted in the following form: 7 Sg?-Ll?,11Sg?-Ll/,9
Sg/-Ll?, and 5 Sg/-Ll/. In 16 of the 32 encounters,
S. globula was the resident spider and in 16 it was the
intruder. At the beginning of the encounter, the new
individual was introduced at 10cm from the resident
spider. The experimental trials lasted at least 60 min,
ending when one spider killed and sucked its prey at
least for 20 min. In case when both were alive at the
end of 60 min, the experiment lasted another 60min. If
neither were attacked or killed, the encounter was con-
sidered a draw.
In the videos, the frequency and the sequence of the
behavioral events during spider interactions were
recorded and analyzed, where an aggressive encounter
was defined as physical contact between the spiders,
resulting in the death of one spider. The description
and nomenclature of behavioral events followed Gilbert
and Rayor (1985) and Ferna´ndez et al. (2002) for the
construction of the ethogram. The 10 behavioral events
considered were—1) Alert posture, 2) Leg retraction,
3) Tapping, 4) Prey palpation, 5) Spitting, 6) Scraping
(reciprocal rasping of pedipalps and cutting the threads
of the web), 7) Reach (prey capture), 8) Roll (envelop-
ing), 9) Biting, and 10) Nibbling. In each experiment,
the death of the spiders and leg loss by S. globula were
recorded.
With the behavioral event sequence that formed the
ethogram, a flux diagram was built indicating the fre-
quency of the events. The frequency of aggressive
encounters in relation to the total number of encoun-
ters was recorded, and the proportion of aggressive
encounters (PA ¼number of aggressive encounters/
total number of encounters) and their confidence inter-
vals (CI
0,95
¼p61.96 H(pq/n)) were calculated. Also,
the proportion of victories of S. globula was recorded
(PV ¼number of victories of Sg/number of aggressive
2J
OURNAL OF MEDICAL ENTOMOLOGY
encounters) with its confidence interval. The effect of
residency (resident vs. intruder) on PA and PV was ana-
lyzed with the Fisher exact test, which provides the
exact P-value (Fisher p) for proportion differences for
small n. The effects of the body mass of S. globula,the
body mass of L. laeta, and the body mass ratio on PA
and PV of each spider was analyzed by logistic regres-
sion. The models were—logit (*)¼b
0
þb
1
M
bSg
, logit
(*)¼b
0
þb
1
M
bLl
,andlogit(*)¼b
0
þb
1
R, where
M
bSg
is the body mass of S. globula,M
bLl
the body
mass of L. laeta, R the body mass ratio, and (*)wasPA
or PV whichever variable was studied. To study interac-
tions between M
bSg
and sex in aggressive encounters
and in victories of S. globula, we consider three body
mass intervals: small M
bSg
<70 mg; medium 70 mg
<M
bSg
<100 mg, and large M
bSg
>100 mg, and we
performed v
2
test in the sex–body mass contingency
tables.
Effect on Cohort Development. Six adult females
of L. laeta with their egg sac were captured and intro-
duced separately in a plastic box of 35 by 25 by 20 cm
3
during summer season. Boxes were held at ambient
laboratory temperatures to simulate that of unheated
houses in Santiago. Temperature and relative humidity
inside the box were recorded with a digital Sychrome-
ter with remote probe AZ8723 (AZ Instruments Corp,
England). The six boxes were maintained with a photo-
period of 12:12 (L:D) h and were placed on a rack and
randomly rotated every 2 wk to avoid effects due to the
particular position of each box. These spiders, with
their egg sacs, were maintained until eclosion of the
spiderlings. Each of the spiders with their egg sacs
were randomly assigned into either experimental
group: Sg(): a group of three cohorts that developed
without S. globula, and Sg(þ): a group of three cohorts
in which an adult S. globula captured in Santiago was
introduced into the box. Beginning at eclosion (day 0),
the spiderlings were inspected and counted every 2 wk,
recording the number of survivors, the dead individu-
als, and the exuvia. The day 0 for each cohort were as
follows: Sg()
1
: December 20; Sg()
2
,Sg(þ)
1
,and
Sg(þ)
2
: January 1; and Sg()
3
and Sg(þ)
3
: February 7.
The dead spiderlings and exuvia were removed. Spider-
ling instars were determined by counting the exuvia
and comparing these with the morphological character-
istics of the spiderlings described by Galiano (1967)
and Galiano and Hall (1973).
At each inspection, the individuals were photo-
graphed at 50cm distance with a reference mark of
known dimensions. At this time, 10 mealworm larvae
(Tenebrio molitor L.) were introduced in the box. These
larvae vary in size during development, so that larvae at
an appropriate size to be handled by the spiderlings (at
most three times their body size) were chosen. Also, 10
drops of water were deposited in the corner of the box
to provide humidity. In the Sg(þ) cohorts, the spider-
lings were initially maintained with their mothers until
the latter was killed by a S. globula.InSg()cohorts,
the L. laeta mother was removed at the date equivalent
to the death of a mother in a Sg(þ) cohort. When the
adult of S. globula died, it was replaced by a new adult
of this species. A total of 11 adult S. globula, 5 females
and 6 males, were used during the experiment. Thus,
Sg(þ) cohorts always had one predator inside the box.
During each inspection, the spiderlings were observed
for 20min, recording and photographing activities such
as predation and cannibalism.
At each inspection, the number of live spiderlings
was recorded (N). From photographs, the body length
(prosomaþopistosoma) of all spiderlings whose posi-
tion permitted measurement was recorded. The meas-
urements were made with ImageJ 1.32 software (NIH).
In each cohort, the number of spiderlings alive on
each count occurrence was divided by the initial num-
ber placed in the box (N/No), and a regression model
was fitted, ln (100N/No) ¼b
1
tþbo. This allowed us to
estimate the mortality rate (m¼jb
1
j). The curves gener-
ated between treatments were compared with
ANCOVA for homogeneity of slopes, considering the
cohorts as the independent variables, ln (100N/No) as
the response variable, and time as the covariable.
Planned comparisons were performed to contrast
Sg(þ) and Sg()cohorts.
Linear regressions were performed between mean
body size (mbs) and time (t) and between maximum
body size (Mbs) and time. The models were
(*)¼b
0
þb
1
t, where (*)wasmbsorMbs,depending
on the variable analyzed. The progression of these vari-
ables was compared with ANCOVA, considering only
the length of the experiment where all cohorts had live
spiderlings (171 d).
Results
Individual Interactions. In the encounters in
which S. globula was the winner, the predator behav-
iors—tapping, spitting, scrapping, reach and roll, biting,
and nibbling—were observed in 100% of cases. Alert
posture was observed in 80% and leg retraction in
40%, (Fig. 1).
Of the 32 encounters, 19 aggressive encounters were
observed: PA ¼0.594 60.087; CI
0.95
:[0.474;0.664].Of
these, S. globula was the winner in 13 of the encoun-
ters, obtaining PV ¼0.68460.106; CI
0.95
:[0.475;
0.893]. Leg loss by S. globula was observed only on one
occasion (3.13%). This individual was killed by L. laeta.
The sex of fighters did not affect the probability of
aggressive encounter. Of the 18 male and 14 female
S. globula used in the study, nine aggressive encounters
were observed by males and in 10 by females providing
a 50% (CI
0.95
: [26.9; 73.1]) and 71.4% aggression per-
centage (CI
0.95
: [47.7; 95.1]; Fisher p ¼0.29). Similar
results were observed with L. laeta wherein eight of 16
aggressive encounters occurred with males (50%; CI
0.95
:
[25.5; 74.5]) and 11 of 16 aggressive encounters with
females (68.8%; CI
0.95
: [46.1; 91.5]; Fisher p ¼0.48).
The sex of fighters also did not affect the probability of
victory. Five male (55.6%; CI
0.95
: [23.1; 88.1]) and eight
female (80.0%; CI
0.95
: [55.2; 100]) S. globula were win-
ners (Fisher p ¼0.35), while three female and three
male L. laeta were winners (Fisher p 1).
TherewerenodifferencesinPAwhenS. globula
was the resident spider, 0.438 60.124, CI
0.95
:[0.195;
0.681] or when it was the intruder: 0.75 60.108,
2015 CANALS ET AL.: S. globula VS.L. laeta 3
CI
0.95
: [0.538; 0.962] (Fisher p ¼0.149) or in PV
between when S. globula was resident: 0.857 60.132,
CI
0.95
: [0.598; 1.000] or when it was the intruder:
0.583 60.142, CI
0.95
: [0.304; 0.862] (Fisher p ¼0.331).
Body mass of S. globula adequately predicted PA
(logit(PA) ¼3.66 þ0.055m
b
,Wald¼4.738, P¼0.029;
probability of good classification (PGC) ¼0.533) and
also adequately predicted PV (logit(PV)¼8.03
þ0.062m
b
,Wald¼3.872, P¼0.049; PGC ¼0.833;
Fig. 2). Interactions between body mass and sex were
not found (v
2
¼2.8, P¼0.24 and v
2
¼2.3, P¼0.32 for
aggressive encounters and victories of S. globula,
respectively). In contrast, the mass ratio R did not pre-
dict PA well (logit(PA) ¼0.727 þ1.138R, Wald ¼1.997,
P¼0.158) or PV (logit(PV) ¼1.332þ2.587R, Wald ¼
1.928, P¼0.165). Also, the body mass of L. laeta did
not predict PA (logit(PA) ¼0.793 þ0.004m
bLl
,Wald¼
0.193, P¼0.66) or PV of this species (logit(PV)¼
1.395 0.004m
bLl
,Wald¼0.431, P¼0.521).
Effect on Cohort Development. The environ-
mental conditions of the two experimental groups were
the same (Fig. 3). In two of the Sg() cohorts, 79 and
106 spiderlings emerged from the egg sac. In the third
cohort, an exceptionally low number of 12 spiderlings
emerged from the egg sac. In Sg(þ) cohorts 146, 81,
and 101 spiderlings emerged from the egg sac.
In the three Sg(þ) boxes, eight adult predator spi-
ders were necessary to achieve the establishment of the
predators. In five introductions L. laeta killed S. globula
(three males and two females) while in the other three
opportunities, three males of S. globula killed the three
established female L. laeta.
After >550 experimental days, all Sg() cohorts had
live adult spiders. In the Sg() containers, the longest
surviving L. laeta had molted up to 10 times and sur-
vived from 517–566d. In contrast, in all Sg(þ) contain-
ers, all spiderlings were dead at 182, 270, and 275 d
post-predator introduction for cohorts 1–3, respectively.
In the latter cohorts only three molts were obtained,
while in the same time frame in Sg() cohorts two to
seven molts were observed among spiderlings.
A higher daily mortality rate of the spiderlings was
obtained in Sg(þ) cohorts (0.020160.001276) than in
Sg() cohorts (0.010572 60.000991; F
5,86
¼3.017,
P<0.001; Planned comparisons: F
1,86
¼20176.7,
P<0.001; Fig. 4). The mortality rates for each cohort
were—Sg()
1
:0.01260.0006 (R
2
¼0.96, P<0.001),
Sg()
2
:0.01160.0013 (R
2
¼0.81, P<0.001), Sg()
3
:
Alert
posture
Leg
retraction
Tapping and
prey
palpation
Reach and
Roll Scraping Spitting
Biting Nibbling
Tapping and prey
palpation (2)
Tapping and prey
palpation (3)
80% 20%
60%
40%
100%
70%
30%
70%
30%
20%
100%
80%
100% 100%
Fig. 1. Ethogram of predatory behaviors expressed by adult S. globula when encountering adult L. laeta during paired
interspecific encounters in 19.5-cm circular chambers.
4JOURNAL OF MEDICAL ENTOMOLOGY
0.006 60.0004 (R
2
¼0.96, P<0.001), Sg(þ)
1
:
0.024 60.0027 (R
2
¼0.86, P<0.001), Sg(þ)
2
:
0.018 60.0027 (R
2
¼0.92, P<0.001), Sg(þ)
3
:
0.022 60.0016 (R
2
¼0.92, P<0.001).
During equivalent time periods, the mean body
length of the spiderlings was similar in all cohorts, but
the maximum body length during this time was
3.92 60.24 mm in Sg() cohorts and 3.17 60.07 mm
in Sg(þ)cohorts(F
1,66
¼55.32, P<0.001). Further-
more in Sg(þ) the variance was lower (Bartlett
test ¼46.2, P<0.001). The slope of maximum body
length increase was different among all cohorts
(F
5,66
¼3.54, P<0.001). Also when Sg() and Sg(þ)
groups were compared, a significant difference was
found (F
1,74
¼25.84, P<0.001; Fig. 5).
Discussion
In studying behavioral responses of S. globula using
a different prey species, Ferna´ndez et al. (2002)
described S. globula as expressing all behavioral dis-
plays reported in this study, but to a greater extent.
For example, in our study alert posture and leg retrac-
tion only were observed in 80% and 40% of cases,
respectively (Fig. 1). Interestingly, of the 10 behavioral
displays described by these authors, we only recognized
eight in an isolated form. Tapping always occurred with
prey palpation, while reach always occurred with roll
and thus were considered a single event.
When a predatory event occurred, the sequence of
events by S. globula was not always the same.
For example, in three of 32 encounters, the tapping
display was repeated alternating with other displays,
such as spitting, reach and roll, and biting. Tapping dis-
play may be part of a strategy destined to ensure the
immobility of the prey before nibbling. Also, during
tapping display S. globula more frequently used the left
first and second leg, than the right legs, agreeing
with that reported by Ades and Ramires (2002).
These behavioral displays, favored by the length of the
legs, could increase its success of survival by reducing
the risk of counterattack during a predatory event.
Spitting is used to immobilize prey (Gilbert and Rayor
1985), increasing the probability of predatory success.
The probability of an aggressive encounter, a situa-
tion where interactions led to the death of one of the
spiders, was only moderate, occurring in only approxi-
mately 60% of the occasions, which may be related to
motivational factors of the predator or the prey. For
example, one evident factor would be the time lapse
since the predator last meal. This factor was partially
controlled by the time of acclimation in laboratory,
which ensured at least 2 to 3wks without prey. Neither
the sex of the predator nor that of the prey, regardless
of which species was the resident, had an effect on the
probability of an aggressive encounter or the
Fig. 2. Logistic regressions between the (A) probability
of aggressive encounter (PA) and (B) probability of victory
(PV) by adult S. globula on the body mass (g) of S. globula
(Mb) in paired interspecific encounters with adult L. laeta in
19.5-cm circular chambers.
Fig. 3. Variation of temperature and relative humidity
during the experimental time in Sg() and Sg(þ) cohorts.
2015 CANALS ET AL.: S. globula VS.L. laeta 5
probability that S. globula was the winner of these
encounters. This probability was only moderately high,
68.4%, which may be a consequence of the fact that
the prey, L. laeta, was a larger and is considered a
quicker spider (Canals et al. 2008) that exceeded by
64% the body mass of S. globula. L. laeta aggressive
behavior was especially striking when encountering S.
globula adults in the three Sg(þ) chambers that con-
tained a L. laeta female with her young. Such a chal-
lenge with spider introductions was previously
described by Canals and Solı´s (2013) who stressed the
special situation represented by a large female guarding
her spiderlings being confronted by a predator. In their
study, they documented the offspring-guarding female
expressing high aggressiveness, and they attributed this
to the likely need for increased food intake leading to
the aggressive behavior and thus becoming a more dif-
ficult prey. This idea is reinforced because the spiders
in general appear to be territorial, especially at low
prey availability (Riechert 1981).
In the individual encounters we only observed a
3.1% leg loss level among S. globula. However in the
Sg(þ) chambers, leg loss occurred in three of eight
encounters (37.5%). Previous reports of encounters
between S. globula and the species L. laeta,L. gaucho,
and L. intermedia suggested a 13.6% leg loss level
(Ades and Ramires 2002), which is between these two
values.
Of all analyzed predictors of an aggressive encounter
and a victorious encounter by S. globula, only the body
mass of S. globula was a good predictor of both PA and
PV. The greater the body mass of S. globula,thehigher
the PA and PV values by S. globula were. The body
mass of the subadults and adults of S. globula used in
this study varied between 23.8 and 123.7mg, and the
variations in mass represented variations in develop-
mental instars. It appears that the effect of the body
mass on PA and PV would be explained by the experi-
ence and ability of the predator acquired during its
development. All individuals of S. globula with body
mass over 85mg had aggressive encounters and all
resulted in winners. (see Fig. 2).
All Sg() cohorts still had live spiders and in all
Sg(þ) cohorts all spiderlings were killed before reach-
ing at most the fourth instar, with a maximum body
size lower than that of Sg() spiderlings after an equiv-
alent time period. Furthermore, the mortality rate in
Sg(þ) cohorts was about twice that of Sg()cohorts.
Predation of spiderlings by the mother was not
observed, contrasting with several predation events on
T. mo l i tor larvae. This fact, the short time that spider-
lings share with their mothers and that this time was
matched for the experimental groups allows to discard
predation by the mother as a cause of differential mor-
tality rate among the experimental groups. The mortal-
ity rate in both experimental groups is explained in part
by natural causes and spiderling cannibalism, which
was observed on two occasions during the inspection of
different cohorts and was described for L. laeta (Vetter
and Rust 2010). Although the actual amount of canni-
balism during the experiments was not recorded
because the boxes were inspected only once every
2 wk, the cannibalism event numbers would have been
similar across the six boxes, because of the similar
maintenance conditions. We believe that the presence
of the predator in the three Sg(þ) boxes did not result
in more cannibalism events due to the sharing of the
larvae with the predator, because S. globula has a
marked preference for less chitinous prey (Fernandez
et al. 2002), and during the inspections when the meal-
worm larvae were introduced the spiderlings immedi-
ately preyed and fed on them.
In the Sg(þ) cohorts, the predation of spiderlings by
an adult S. globula was added to these causes of
mortality, and was directly observed on three occasions
during the count of the spiderlings. Thus, the difference
in mortality between the experimental groups is attrib-
utable to predation and represents the maximum poten-
tial effect of S. globula on the mortality rate of cohorts
of L. laeta. Provided our experimental design, the differ-
ence in the body size between the spiderlings of the
experimental groups and the absence of later instars in
the predator-positive treatment are likely explained by
predation of the larger individuals by S. globula.
Fig. 4. L. laeta spiderling cohort survival rate, expressed
as (ln(100N/No)) in chambers without S. globula (Sg()) and
in chambers with one adult S. globula (Sg(þ)).
Fig. 5. Regression lines between the maximum body
size (Mbs) of L. laeta spiderlings without a S. globula (Sg())
(Mbs
1
) and with S. globula (Sg(þ)) (Mbs
2
) and time.
6JOURNAL OF MEDICAL ENTOMOLOGY
In Chile, S. globula is found inside human dwellings,
alone or coexisting with L. laeta (Fernandez et al. 2002,
Canals and Solis 2013). In other countries, S. globula
has been reported outside of human dwellings, as a
peridomiciliary spider (Fisher and Vasconcellos-Neto
2005a,b). Spiders of the genus Loxosceles frequently
are found with other spider families such as Pholcidae,
Theridiidae, Salticidae, and Selenopidae, but the inter-
action of members of these families with Loxosceles
species has been poorly studied (Sandidge 2004,Fisher
et al. 2006). In Chile, only S. globula has been reported
as a predator of L. laeta (Fernandez et al. 2002,Canals
and Solı´s 2013). Interactions between L. intermedia
and Pholcus phalangioides (Fuesslin) have been
studied in Brazil. Loxosceles species were frequently
found in the web of P. phalangioides, but without clear
population effects (Fisher and Krechemer 2007). These
authors found that P. phalangioides preyed on adults
and spiderlings of L. gaucho,L. laeta,andLoxosceles
hirsuta Mello-Leitao. Sandidge (2004) reported preda-
tion of L. reclusa by three cosmopolitan, synanthropic
spiders: P. phalangioides (Pholcidae), Achaearanea
tepidariorum (Koch) (Theridiidae), and Steatoda trian-
gulosa Walckenaer (Theridiidae), reporting that only
the latter two spiders had a negative, but nonsignificant,
population relationship with L. reclusa.Sandidge (2004)
did not find individuals of L. reclusa in P. phalangioides
webs, a fact that he explained by a different spatial dis-
tribution of the species; L. reclusa was found in webs at
floor level, and P. phalangioides was found in webs in
high corners near the ceiling of the rooms. However,
Fisher and Krechemer (2007) reported that this fact
might be explained by the custom of P. phalangioides of
removing and rebuilding their webs.
Food availability may be an important factor to
explain the results of Fisher and Krechemer (2007) and
Sandidge (2004), because the spiders studied by these
authors are opportunistic spiders that usually feed on
insects. In contrast, although S. globula feed on insects
such as Diptera, Lepidoptera, and Mantodea, it is
mainly an araneophagic spider that preys on several
Loxosceles species and other spiders such as Salticidae
and spiders of the genus Drassodes (Jackson et al.
1998,Ades and Ramires 2002,Fernandez et al. 2002,
Canals and Solı´s 2013).
In Chile, S. globula shares the habitat and the pre-
ferred microenvironments with L. laeta inside human
dwellings, preying naturally on L. laeta (Fernandez
et al. 2002,Canals and Solı´s 2013). Thermal preferen-
ces and desiccation tolerances suggest that the species
share >80% of their thermal niche (Alfaro et al. 2013,
Canals et al. 2013). Both species are nocturnal, making
encounters between them highly probable. This study
showed that on most occasions this encounter has a
favorable result for S. globula. But also, in a consider-
able proportion of interactions, L. laeta preys on
S. globula. Our results demonstrate that under the lab-
oratory conditions used herein, S. globula preyed on
spiderlings of L. laeta, with a clear effect on the mortal-
ity rate of cohorts of this species. However, there is a
report of coexistence of adults and spiderlings of both
species in areas smaller than 1m
2
(Canals and Solı´s
2013). These findings suggest that S. globula is
naturally interacting with the population of L. laeta in
central Chile. The population regulation of L. laeta by
predation would be important because this species, in
the absence of predation, has a high basic reproductive
rate, Ro ¼2.1, and it can maintain large populations
with high dispersion capacity (Canals and Solı´s 2014).
However, according to our results, although S. globula
may impact the number of spiderlings and adults of
L. laeta and perhaps other Loxosceles species in a
coexisting environment, S. globula is not an efficient
biological control agent suitable for Loxosceles species
management. Its presence, however, together with
other control measures such as hygiene and cleaning of
infested rooms, may help to decrease loxoscelism
incidents.
Acknowledgments
We thank Lafayette Eaton, reviewers and the editor for his
useful comments on the manuscript. This work was funded
by Fund for Science and Technology of Chile: FONDECYT
1110058
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Received 30 March 2014; accepted 3 December 2014.
8JOURNAL OF MEDICAL ENTOMOLOGY
