A Trap to Capture Burrowing Arachnids

3 Pages·1991·1.1 MB·English

by  Johannes R Henschel

1991. TheJournal ofArachnology 19:150-152
RESEARCH NOTES
A TRAP TO CAPTURE BURROWING ARACHNIDS
In studies of population biology, it is often surroundings. Current techniques for capturing
necessarytodeterminesizeandreproductivesta- burrowing arachnids, however, often involve
tus of individuals and to mark them for later disturbance, such as excavation. This destroys
recognition. Thisprocessshouldassure minimal burrows and risks injuring animals.
disturbanceofstudysubjectsandoftheirnatural Several alternative techniques for capturing
burrow;C,dooroftrap; D,door-lever; E, balancingshaft; F, trigger-lever;G,trigger; H, lockinghook; I, spider;
J, open vial to provide spider with shelter; K, slit to lock shaft; L, vial with live bait.
150
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RESEARCH NOTES 151
large, burrowing, wandering spiders were tested
inapopulationstudyofLeucorchestrisarenicola
Lawrence, a heteropodid (Henschel 1990).
When disturbance caused by excavation proved
unacceptable, pitfalltrapswereemployed. Trap-
ping success was, however, low because spiders
usually detected and circumvented the edges of
pits. Furthermore, individual spiders could not
be targeted.
Therefore, I designed a container trap, de-
scribed here, which is cheap to make and easy
to operate. It capitalizes on a spider’s tendency
to probe when surrounded by a container. This
probing mechanically triggers closure ofan ar-
tificial trapdoor that prevents the spider from
retreatingintoitsburrow,thuscapturingitinside
the container.
The sensitive trigger mechanism enables one
to capture burrowing arachnids having a mass
of0.5 g or more. I have used it to capture more Figure 2.—Closeddooroftrap locked into place by
than 100spidersoftwospeciesandonescorpion a wire hook.
on surface slopes of0-30° and in winds of0-5
m/s. The trigger is positioned away from the door
The body of the trap (Fig. 1) is made of a so that the spider(I) does not obstruct the slam-
rectangular, flat-bottomed container (base ±1 mingdoor.Althoughaspideriscapableoflifting
X 20 cm, height ±5 cm)with a transparent, air- thedoortoenteritsburrow,itcannotatthesame
tightlid. Acommerciallyavailable 2-literplastic timeliftthelockinghookandthedoor. Deprived
container for food, such as an empty ice-cream ofothershelter, it readily enters a darkened vial
tub, is suitable. All other components besides (J) extending through the side ofthe trap. This
samplevialsaremadeof1.5-mm-gaugestiffwire tube is later removed to manipulate the spider.
and tape. The trap has to be opened to set it. As the
Thedescriptionofcomponentsrefersto labels trigger is very sensitive to wind until the lid is
on Figure 1. A hole of4 x 4 cm (A) is cut into closed, the balancing shaft can be locked into
the bottom near one end ofthe container. This position by forcingitinto the narrowesttoppart
holeislargerthanthenaturaltrapdoorofaspider ofaslit(K)inthewallofthetrap. Whenthetrap
burrow entrance (B) and is covered with a stiff is set and the lid closed, the balancing shaft is
5x5
wire-rimmed cm door (C), hinging on a loosened by lowering it into a wider section of
straightpiece ofwireattachedtothe bodyofthe this slit until the balancing shaft is held only by
trap. The door is held open by leaning a door- the trigger-lever.
lever (D), fixed to one side ofthe door, against Several factors increase trapping success.
a balancing shaft (E) suspended across to the Movements oflive bait placed in a vial (L) out-
otherend ofthetrap. The heavierproximal end side the trap attracts the spidertowardsthe trig-
ofthisbalancingshaftrestson a trigger-lever(F) ger. To overcome the spider’s initial reluctance
connected to a wide, low-hanging trigger (G). to step onto the artificial surroundings, the floor
The trigger-lever and door-lever are circular ofthe trap is covered with sand. On slopes, the
sothattriggersensitivityislessdependentonthe triggershould be downhill ofthedoor. In windy
extent ofoverlap ofcontact points. Ifthe trigger conditions, shifting ofthe trap is prevented by
is pushed only lightly (<0.1 g force = 9.806 x pegging it through its base behind the trigger.
10 ’ Newtons), the heavierend ofthe balancing Weight of the trigger and shapes of door- and
shaftdropsoffthetrigger-lever,movingthedistal trigger-levers determine the minimum size of
end clear ofthe door-lever and the door closes arachnids that can be captured.
by gravity. Simultaneously, a broad hook (H) I thank the Foundation for Research Devel-
drops onto the door to lock it (Fig. 2). opmentforfunds, the Ministry ofWildlifeCon-
152 THEJOURNALOFARACHNOLOGY
servationandTourism ofNamibia forfacilities, Museum Monograph No. 7. Transvaal Museum,
T. Harms for help and M. Seely for comments. Pretoria, pp. 115-127.
REFERENCES CITED
Henschel, J. R. 1990. The biology of Leucorches- Johannes R. Henschel: Desert Ecological
tris arenicola (Araneae: Heteropodidae), a burrow- Research Unit of Namibia, P.O. Box 1592,
ingspideroftheNamibDesert.InCurrentResearch Swakopmund, Namibia
on Namib Ecology—25 Years of the Desert Eco-
logicalResearchUnit. (M. K. Seely,ed.).Transvaal Manuscript receivedMay 1990, revisedAugust 1990.