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07 December 2001

How to Capture Insects

by Rick Imes
adapted from The Practical Entomologist

There are many methods of capturing insects, and any one is acceptable as long as it is safe and does not damage the insect. Many insects are easily collected by hand, with forceps, or by simply clapping a jar over them. Others require a bit more finesse and some basic tools. The following are a few such devices that are either simple to make or else inexpensive to buy.

Nets

Many insects are adept at evading or escaping predators and can easily evade our clumsy efforts. Others can be dangerous to handle; bees and wasps inject venom as they sting, and many of the larger true bugs can deliver a painful bite. For these, and for insects that hide in tall grass or underwater, we need a net, of which there are three basic types.

An aerial net, with which most of us are familiar, is used for netting flying insects out of the air. It is a long sack of soft nylon, organdy, or silk netting that will not normally damage specimens. This delicate material does not wear well and should not be used to capture insects in vegetation or on the ground. After netting an insect with an aerial net, give the handle a quick half-twist to double the net over the opening and prevent escape. The best way to retrieve your catches is by inserting a jar into the net and trapping the insect between the netting and jar.

Sweep nets are made of heavy white muslin or canvas and are used with a sweeping motion to capture unseen insects in tall grass or weeds. This "shotgun technique" rarely fails to turn up something of interest. It is especially useful in meadows during the summer and fall.

A dip net is a long-handled tool used to capture aquatic insects. It has a flat side that may be placed against the bottom of a stream or pond. The triangular hoop is threaded through a tube of heavy muslin with a screen of heavy nylon netting on the end, to allow water to flow through. Insects may be difficult to see among aquatic debris, so you may need to dump the contents into a white tray and watch for movement.

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Beating tray

Insects that frequent plants are often reluctant to fly or run, preferring instead to remain still and rely on their natural camouflage and small size to escape detection. A sweep net, good for grassy meadows, does not work as well on trees and shrubs; here you need a beating tray. This is a simple affair made of white cloth stretched over a frame of two crossed sticks. (A light-colored umbrella also works well.) It is held or placed under a shrub or tree branch, to which you deliver several sharp blows, taking care not to damage the plant. Insects having taken refuge there will fall onto the beating tray and can then be collected by hand or other means.

Pitfall traps

Pitfall traps are effective in catching insects that scurry across the ground rather than fly. Simply dig a small hole with a garden trowel and sink a jar or cup in it so that the top is flush with the surface of the ground, filling in with soil around the outside of the container. An inch of 30 per cent water to 70 per cent alcohol mixture in the bottom will kill the insects if you do not wish any to escape. If you do not want to kill any insects, use yogurt pots with drainage holes and check every few hours. Place three or more strips of wood radiating from the rim like the spokes of a wagon wheel; these will guide insects into the trap. Cover the trap with a slab of wood or stone to keep out rain water, and check it daily. You should set several traps in a variety of a locations in order to find the best sites in a given area.

Bait traps

One of the major pastimes of insects is searching for food, and many species can be lured with bait. Pitfall traps or small containers suspended from a tree branch make excellent bait traps. Cover them securely with a large-mesh screen with openings about 2 cm square to admit large insects but keep out other scavengers.

A mixture of equal parts of molasses and water makes a fine bait. Add a little yeast and allow the mixture to ferment for a day or two before baiting traps with it. A mash of fermenting fruit also works well. Cloth strips soaked in a bait mixture and suspended from a tree branch will attract larger insects, such as nocturnal moths, that cannot fit through the screen covering your other bait traps. The mixture can also be painted onto the bark of a tree. Visit the site every hour or so during the night.

Decaying animal remains or meat scraps will attract many species, especially beetles and flies. If you wish to kill your prisoners, suspend the bait in a cheesecloth sack from the wire screen and put an inch of the water and alcohol mixture in the bottom of the trap. Dung is also a very effective bait, but take precautions against the transmission of disease or parasites by handling it only with disposable implements. The water and alcohol mixture in the trap should sterilize any specimens attracted to the dung.

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Berlese funnel

More insects than you might have guessed reside in the cool, moist debris littering a forest floor. A Berlese funnel is a device that can drive insects from such material. Simply place a large funnel, one that narrows to about a two centimeter opening, small-end down in a tall glass jar containing a layer of moistened paper towels. Fill the funnel with leaf litter and suspend a highwattage light bulb over it. As the debris warms and dries, any insects it harbors will burrow deeper, seeking their preferred conditions, until they reach the funnel opening and fall into the jar.

Sifter

A sifter will do much the same job as a Berlese funnel. To make one, cut the bottom from an old bucket, leaving about a one-inch lip. Cut a circle of large wire screen to rest in the bottom of the bucket. Fill the sifter half-way with debris and cover with canvas, securing the cover with cord or a large rubber band. Shake the sifter vigorously over another bucket or other deep container and collect your specimens.

Light trap

It's common knowledge that nocturnal insects are attracted to light, and you can use this behavior to your advantage. There are many different types of light traps. Perhaps the simplest is a white sheet tied at all four corners and suspended vertically, with a lantern shining on it from behind. As insects alight on the sheet, they may be simply scooped off with an aerial net, allowing you to capture only the ones you want. An empty Berlese funnel with a cylinder of wire screen extending up around the light bulb also makes an effective light trap, though you may need to adapt it by using a funnel with a larger opening at the bottom.

An aquatic light trap can be made with a flashlight, a watertight jar, a length of pipe about six inches in diameter, and some fine-mesh wire screen. Turn on the light; seal it in the jar, and place it in the pipe. Use the wire screen to cover the end of the pipe toward which the light does not point, and fashion a funnel out of the same material for the other end, pointing inward. Secure the pipe with strong cord and lower it into the water, with the funnel facing upstream if there is a current. You may need to weight it down with rocks if the pipe is not heavy.

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Aspirator

Some insects that you will find are so small that they cannot be easily collected by hand or with a net. For these, the best method may be the use of an aspirator, with which you manually suck the insects into a small vial.

You can make an aspirator from any small vial with a tight-fitting cap or stopper, two plastic straws, and a length of flexible plastic or rubber tubing. Drill two holes, exactly the same diameter as the straws, in the cap. Insert one straw so that it is about one centimeter above the bottom of the vial. Cut a short piece from the second straw and insert it so that about two centimeters extends into the vial and one centimeter protrudes above the cap. Seal the joints between the cap and straws with silicone bathtub caulk. Cover the inside of the short straw with a small piece of fine netting so that you don't accidentally suck insects into your mouth. Attach one end of the rubber tubing to the other end of the short straw, seal with silicone caulk, and you're ready for action. Turn over stones or sift through forest and plant debris to suck up little insects like springtails.