Acta Zool. Fennic'a 190:267-272
December 1990 ISBN 951-9481-35-4 ISSN 0001-7299
© 1990 Finnish Zoological Publishing Board
Arachnology, Turku, Finland,
Brood care and family cohesion in the tropical
scorpion Pandinus imperator (Koch)
ZooloRisches Institut (lll) der Universität, RöntgenrinR 10, D-8700 WürzburR, FRG
Pandinus imperator is a forest dweller
tropical West Africa. In the field,
the laboratory, mixed age groups
also unrelated animals lived jointly in terraria rarely showing within-group aggression
the mother influenced growth rate and survival probabil-
the young. With birth, mothers became very aggressive.
To study family cohesion
Pandinus, experiments with family groups were con-
ducted. Siblings aggregated around their mother. In choice experiments with two fam-
ily groups, mothers were placed in enclosures that only the young were able to enter or
to leave. Second instars significantly preferred the enclosure containing their own
mother. Aggression among unrelated young
the same age was not observed.
Feeding experiments studied the possible advantages
long-Iasting group living
with regard to enhanced success in prey capture and its effect on growth
second instars were unable
subdue large prey on their own. Sibling
groups with their mother removed suffered high mortality due to starvation and canni-
balism compared to groups with mothers present. Here, young grew significantly faster:
they shared the prey that only the mother was able to kill and dismember. Pandinus
imperator has to be considered an intermediate subsocial scorpion.
Only a few arachnid species exhibit social be-
havior (Buskirk 1981).
scorpions, 'social phases'
are normally restricted to interactions during
lFonnerly Dieter Krapf.
mating and the maternal care
birth to shortly after the first molt. There are,
however, several reports
pions in the field, consisting partly
related individuals. These ob-
servations, summarized by Polis &
(1986) suggest that living in a group may be an
some scorpion species. The
care in Pandinus
ACTA ZOOL. FENNICA Vol. 190
following study describes experiments on group
behavior in Pandinus imperator (Koch) (Scorpi-
onidae), a ground-dwelling scorpion inhabiting
rain and gallery forests
tropical Africa. In
Pandinus, group behavior appears to be more
highly evolved than in most other scorpions.
2. Materials and methods
Pandinus imperator were collected
in a secondary forest in the Ivory Coast/West
Africa. All young used for laboratory experiments
were bred in captivity. The scorpions were indi-
vidually paint-marked. They were kept at a rela-
at least 90% and a temperature
23°C (night) to 26°C (day). For further details on
breeding conditions, see Krapf (1988).
Aggregation experiments with two (unrelated)
Pandinus (second instars and
their mother) were performed in an arena (I m2)
with four shelters
cm), one in each
corner. Before each trial, the soil in the arena was
mixed and shelters were interchanged. Late in the
afternoon, the scorpions were released into the
the arena. They were active only at night.
By sunrise, at the latest, all were hidden
shelter. To enclose an adult female, a plastic
was turned over each
shelter. Small horizontal slits in the container
walls allowed young scorpions to enter such shel-
ters, but prevented the female from leaving them.
The females were randomly distributed into the
enclosures. The scorpions found
ter were counted about 24 ho urs after release
(specimens were never found outside a shelter).
The experiments were repeated
and the data pooled thereafter (the experimental
conditions were always the same). Forevaluation
always referred to the shelter
where the mother was found. The other shelters
and 4) were ranked
the total number
young which were counted in
each during the entire experiment. The observed
animals was tested against a uni-
For feeding experiments, the second instars
a female were randomly allotted to one of the
a) mother present; live prey offered,
b) mother absent; live prey, and
c) mother absent; dead prey (which was killed
For evaluation, the data
two parallel experi-
ments (two family groups with instars
age) were pooled. The scorpions were fed adult
the Argentine cockroach B laptica dubia
(2.35±0.27 g body weight, N=66). The mean body
weight in second in star Pandinus was 0.33±0.05
g (N=34) and 29.96±6.51 g
female Pandinus (N=5). Groups were separately
kept in cages (40x30x20 cm) with a water dish
and a hiding place. About once every ten days all
three groups were simultaneously offered one
Blaptica. The cages were checked daily. Cock-
roaches not eaten one day after feeding, as weil as
prey remains, were removed. Before and after
feeding, all scorpions were weighed on a Mettler
laboratory balance. Mean weight ± standard de-
viation are reported.
Behavioral responses of female Pandinus imperator stimulated
brations. Eight adult females without offspring and family groups (four mothers with second
instars) were tested. Statistics: X'=97.08, df=2; P<0.0001 (mxn-contingency table).
Female behavior (% responses)
No response, Orientation Attack,
State of female escape, defense movements stinging n
no offspring 70.3 28.1 1.6 64
Mother (N=4) with
second instars 7.8 48.4 43.8 153
ACTA ZOOL. FENNICA Vol. 190 • Mahsberg: Brood care in Pandinus imperator 269
N refers to the number
individuals tested, n
to the numberof observations. For statistics, Mann-
Whitney V-test, Kruskal-Wallis H-test and X2-
tests were used (see Sachs 1984).
3.1. Female behavior
the largest extant
scorpion species, and probably the heaviest (Krapf
1988). Normally, these scorpions do not react
aggressively when touched, contrary to buthids
like Androctonus. However, after delivering its
young, the Pandinus female's behavior changes
significantly (Table I); the same was observed in
Heterometrus spp. Both scorpionids, which re-
spond very sensitively to substrate vibrations
(Krapf 1986a), were stimulated by scratching the
ground with a pair
pincers. Females without
young tried to escape or showed defensive pos-
tures in most cases.
contrast to these non-
aggressive individuals, mothers with offspring
turned quickly towards the stimulus source. In 67
cases, they vigorously grasped the
forceps or even tried to sting, which
unusual for Pandinus imperator. In this situation,
intruding conspecifics were sometimes seriously
injured. Potential prey was always captured. Sur-
prisingly, young were never harmed
such fights, though they often were in close
contact even with their mother' s snapping chelae.
The quick discrimination between intruder, prey,
and offspring was probably mediated by the
numerous chemosensitive hairs on the pedipalps.
prey in scorpions following
contact with the chelae has been demonstrated
earlier (Krapf 1986b). Females
carpathicus (L.) recognize their young through
chemical scents (Vannini et al. 1978). But, as in
most other scorpion species, maternal behavior in
Euscorpius normally ends within a few weeks,
shortly after the first molt
the young. In
Pandinus, however, at least under laboratory
conditions, the female tolerates young, which are
months old. They are still associated with
their mother. Especially for younger stages, the
the female probably pro-
vides protection from predators, which are nu-
merously reported for scorpions (Polis et al. 1981).
3.2. Family cohesion
About a week after the first molt, the second in-
stars leave their mother's back.
large terraria with many hiding places
the young were norrnally found in close contact
with their mother. The aggregation tendencies
second instars and their mother were tested in an
arena. In the first experiment, mother and young
were free to choose one
shelters (Table 2).
This experiment was repeated twelve times con-
144 young tested, 48.6% aggre-
gated under the female's shelter. The observed
distribution to the four shelters is significantly
different from a uniform distribution (X2=85.72,
In the field, offspring probably
leave their mother rarely before finally dispers-
ing. The same is reported in the burrow-inhabiting
Scorpio maurus (L.) (Shachak & Brand 1983) and
in Didymocentrus caboensis (Williams) (Polis &
Did the Pandinus mother act as an attractant
that promoted aggregations
the young? To an-
swer this question, the female was put in an
enclosure. Table 3 shows the distribution
second instars (N= 12,
trials), which could
Aggregation behavior of a family group of
Pandinus imperator (mother with 12 second instars).
All animals were free to choose a shelter. Shelter M
which the mother was found. After each
trial all scorpions were released into the center of the
arena; data from 12 trials are pooled.
Statistics: X'=85.72, df=3; P<0.0001 (x'-test).
2 3 4 n
% aggregated 48.6 38.9 10.4
Aggregation behavior of 12 second instars of
Pandinus imperator, which were free to choose one of
four shelters. The mother was enclosed
After each trial all young were released into the center
of the arena. Data from 14 trials are pooled.
Statistics: X'=164.24, df=3; P<0.0001 (x'-test).
2 3 4 n
% aggregated 63.7 29.2 6.0 1.2 168
care in Pandinus
ACTA ZOOL. FENNICA Vol.
related lamily groups
arena with lour shelters. The moth-
both lamilies were each enclosed under a
shelter; two enclosures were empty. The distributions
'green' and 'yellow' offspring are signilicantly differ-
ent (X'=7.84, df=2, P=O.02; mxn contingency table).
freely move around the
tested, 107 (=63,7%) preferred the mother's en-
closure_ This result differs significantly from the
suggests that the hiding place
the mother at-
tracts young scorpions, which appear to search for
it their mother they try to find; can they
discriminate between their own and an alien
a choice experiment, two unreiated
family groups (female and offspring) were tested.
The specifically paint-marked second instars
the two families were comparable in age and size
0.349±0,026 g, N=I2; V-test
me an weight:
1.51, n,s.), The two females were
enc10sed under separate shelters. The 29 off-
spring, which never showed any sign
miliar aggression, were jointly released into the
arena. The young had the opportunity to choose
between the two mothers' places and two empty
shelters, The result (pooled data from
shown in Fig.
and 'yellow' instars is significant
P=0.02; mxn-contingency table). The offspring
both families aggregated
half (' green') and
ofpossible cases (n=204
144) undertheir own mother' s shelter. A mother
never harmed alien offspring,
the field, P andinus
imperator were found
mixed age groups, which
at least partly appeared to be family groups.
still unc1ear whether different family groups may
occur in c10se vicinity under one log or in one
termite mound, which are the preferred shelters of
P andinus. U nder these circumstances, however, a
the mother may be
adaptive for the offspring, to avoid intraspecific
predation by males
non-gravid females (Van-
nini et al. 1978).
3.3. Feeding experiment
the laboratory, I often observed groups
Pandinus and Heterometrus jointly
killing prey. Second instars tried to attack large
insects also, but normally they did not succeed in
subduing large prey, It was assumed that the
the mother is advantageous to the
youngs' access to food. To test this hypothesis,
Pandinus imperator, with their
mother present (a) or absent (b, c), were offered
very large prey that were live in two treatments (a,
b) and dead in the other (c), Up until this time, the
offspring had never been fed, The growth
young from the age
86 days to 276 days in
b, and c
shown in Fig.
Most strikingly, all offspring in group (b) did
not survive past 157 days; they never succeeded in
killing a cockroach and starved to death.
eral, cannibalism is very low in Pandinus, but in
(b) four young were eaten by siblings (compared
to one case
group a). From the age
body weights in
highly significant (H= 14.31 to
16.57, dj=2, P<O.OOl; H-test). There
ence in me an body
to 0,85, V-test, n.s,), Though both groups were
offered the same amount
food, one should keep
in mind that in group (a) the mother was present,
about a hundred times heavier than
N = 8
Growth and age of second instar Pandinus imperatorduring a feeding experiment. The mean body weights
of three groups are compared. The mother was present in one (black) and absent in two groups (dotted/striped).
About once every ten days all groups were offered one large adult female cockroach (Blaptica dubia), which
two (blackldotted) and dead (striped) in one treatment. Standard deviation of the mean is indicated by line
at top of bar. Statistics: H-test (*
ear1y second instar. In fact, in the seven months
the experiment, the female ate very little.
other hand, the cockroaches were seized and
crushed exclusively by the mother. An analysis
prey remains in the field has shown that the
Pandinus' diet consists
diplopods and large beetles. These arthropods are
large prey, difficult and dangerous for individual
young scorpions to subdue even in a group,
easily killed by adults. As shown in group c,
scorpions may feed on dead prey, too, which
probably is rarely found in nature by juvenile
scorpions. In the laboratory, groups
young Heterometrus spinijer (Peters) jointly fed
on dead cockroaches and even on a dead young rat
they had dragged into their shelter
Dismembering the carcass was rendered possible
only by cooperation. The behavior exhibited
Pandinus and Heterometrus resembles the group
mimosarum Pavesi (Ward & Enders 1985). In this
genus, cooperative brood care is highly developed
(Seibt & Wickler 1988).
Acknnwledf!,ements. I am indebted to K.
Polis for valuable comments on the manuscript. I
would also like to thank Petra Eichler and Loretta Rott for
1981: Sociality in the arachnida. -In:
(ed.), Social insects 2:281-367. Aca-
demic Press, New York.
1986a: Verhaltensphysiologische Untersuchun-
gen zum Beutefang von Skorpionen mit besonderer
Berücksichtigung derTrichobothrien. -Doctoral thesis,
Universität Würzburg. 211 pp.
1986b: Contact chemoreception
prey in hunting
scorpions. -Zoo!. Anz. 217: 119-129.
Fortpflanzung, Wachstum und
Haltung. -Herpetofauna (Weinstadt) 56:24-33.
1986: Sociality among
scorpions. -Actas X Congr. Int. Aracno!. Jaca/Es-
A., Sissom, W.
scorpions: Field data and a review. -
Arid. Env. 4:309-326.
Sachs, L. 1984: Angewandte Statistik. -Springer Verlag,
Berlin. 522 pp.
Mahsberg: Brood care
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& Wickler, W. 1988: Bionomics and social struc-
the genus Stegodyphus, with
special reference to the African species
mimosarum. -Verh. Naturwiss. Ver. Hamburg,
Shachak, M. & Brand,
1983: The relationship between sit
and wait foraging strategy and dispersal in the desert
scorpion, Scorpio maurus palmatus. -Oecologia
Vannini, M., Ugolini,A. & Marucelli,
some Euscorpius (Scor-
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