Collecting techniques

Visual Search, Sweeping, Beating, Pitfall Trapping, and Litter Sampling

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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.

  5. 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.
  6. 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 collecting!

  7. 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 ground.

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 Funnel.

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last revised 29 February 2000 / prepared by Clay Harris