Visual Search, Sweeping, Beating, Pitfall Trapping, and Litter
The easiest way to capture and collect spiders is to scare them into a dry
container (such as the empty film canisters) and then transfer them into a
container with alcohol. Alternately the film canister can be placed in a freezer
for a few minutes. In the freezer the spider will enter torpor and die
relatively quickly and may experience less trauma. Carbon dioxide gas can also
be used to anesthetize spiders before collecting. The following are a few
basic methods used when collecting spiders.
- Visual Search. Walk through the habitat and search visually for
spiders, their webs or retreats (curled leaves, silken cases). Walk or crawl
low through the habitat checking under loose bark, fallen wood, debris,
rocks etc. Always remember to return the fallen logs or rocks to the same
position where you found them. These micro habitats can be very important to
small animals, so it makes sense to minimize your disturbance impact. Walls
of houses, buildings and especially basements are also excellent spider
hunting grounds. This method can be especially interesting at night because
a completely different fauna emerges after dark.
- Sweeping. Using a heavy insect net (or even a pillowcase stretched
over a wire clothes hanger) sweep through the top foot of loose soft
vegetation or tall grass. Don't
try this where there are berry vines or roses because the net will snag and
the spiders will escape. Remember to use quite a bit of vigor as you sweep
or the spiders may fall off the vegetation in front of your net. After a few
(dozen?) sweeps, dump the contents of the net onto a flat sheet and capture
the spiders as they run away. Be prepared to act quickly! Sort carefully
through the remaining material, you may find a number of spiders curled up
and "playing possum" among the debris. It is not uncommon for a
sweep sample to capture a dozen species representing four to seven families
after a few minutes of work. This is one of the best methods of capturing
active hunters such as jumping, lynx, nursery-web, sac or ghost spiders.
Small web-building species are also frequently captured.
- Beating. This method is much like sweeping. In this case spread the
cloth sheet under a bush or the low branches of a tree. Grab the branches
and give them a vigorous shaking, alternately strike them with a stick or
stiff branch. Spiders (and other creatures) will be dislodged and will fall
onto the sheet. As before, be ready because they will move quickly to hide.
Some spiders may return to the branch up a silk drag line that they left
when they fell.
NOTE: Beating and Sweeping do not work well in wet
conditions. If there is a heavy dew or if it has rained recently the net and
the spiders will stick to the wet cloth and are often damaged or killed during
the sweeping. They are much less likely to tumble into the net. Avoid sweeping
in such conditions.
- Pitfall Trapping. One of the most effective methods of capturing
ground-living spiders is pitfall trapping. Any smooth-sided container buried
flush with the ground surface will work. Some people prefer to have a funnel
at the top of the container and the plastic "disposable"
cone-shaped plastic cups can be modified for this purpose. Inside the pit
you may want to put a second cup so that you can remove the contents without
disturbing the edge of the pit. This edge is probably the most crucial key
to success. If a spider detects a lip or a ridge, she is likely to walk
around rather than tumble into the trap. Rain can be a problem so you may
wish to place a cover over the pit propped up about an inch or so above the
edge. The smaller the gap between trap and lid will reduce accidental
captures of small vertebrates (toads etc.). Sometimes pits are left
"dry" but most collectors use ordinary auto antifreeze in the
pits. This will kill and preserve the captives with minimal evaporation.
Both methods have potential problems. If you leave pits dry you may find
only one large (well-fed) spider or centipede, smaller ones will have been
killed and/or eaten. If you use wet pits the fluid may attract wildlife
which could be poisoned. Antifreeze is available in two forms: ethylene
glycol-based and propylene glycol-based. Propylene glycol is preferred
because it is not as toxic. If you do use a toxic liquid in your pits you
must cover the pits with wire screen or other barriers to keep wildlife out.
If you put out pit traps you should be prepared to check them frequently.
Some nocturnal raiders may dig up and destroy your pits. Raccoons, skunks and
opossums are infamous for this behavior. To prevent this, cut a piece of
"chicken wire" screening about 2 feet square. Place over your pit
and pin down the four corners with tent stakes or heavy bent wires. The mesh
is wide enough that small creatures (such as spiders) will pass through
undisturbed and the edge is usually far enough from the trap that it will
discourage inquisitive raccoons from attempting to tunnel into the trap.
Remember to remove the pit and re-fill your hole when you are finished
- Litter Sampling. Using gloves, collect a large amount of leaf
litter in a black plastic trash bag or similar container. Be sure to include
the leaves and duff at the surface of the soil as this will have many small
animals. Keep the bag of litter cool until you are ready to extract the
spiders. A litter sample left in the sun will bake and the dead spiders will
be impossible to find. Our standard sample unit is 1 m2 area of
Berlese Funnel method: place the sample over a large funnel that has been
fitted with a 1/4-1/2 inch hardware-cloth or wire screen. The funnel should be
placed in a rack with the opening over a cup with alcohol. Suspend a bright
light over the top of the leaf litter (not too close, leaves burn!). In the
laboratory we use a 90W bulb but always ensure that the bulb is at least
3 inches away from the top of the litter. If you use a 25W or 40W bulb you can
place the bulb a bit closer but never let it touch the leaves. As the
pile of leaves dries out the small organisms will migrate down and eventually
fall through the funnel into the alcohol-filled cup. Crude illustration of a Berlese
Specimens & Collecting Spiders
for Preserving Spider Specimens
to Study Spiders
in Ohio homepage
last revised 29 February 2000 / prepared
by Clay Harris