How To Collect and Preserve Insects for Study

Paul W. Oman.

The equipment used in collecting insects is simple and inexpensive. The average collector usually will need only a few items: Nets, killing bottles, suction bottle, tweezers, scissors, small brushes, and insect pins. Many collectors prefer to make most of their own equipment even though most items may be purchased from commercial supply companies.

The insect net is essentially a cloth bag hung from a loop that is attached to a handle. The size, shape, and material of the net depend on its use.

The beating net (fig. 1) must be strong enough to stand rough use. A handle of straight-grain hickory or ash, such as a hoe handle, fitted at one end with a metal ferrule (fig. 1, C) about an inch in diameter to hold the wire loop in place,is recommended. The handle should be about 1 3/8 inches in diameter and 3 1/2 to 4 1/2 feet long.

The wire loop (fig. 1, A) should be of No. 12 steel wire (0.189 inch in diameter), although even heavier wire is sometimes preferred. After the loop is shaped, it can be tempered so that it will spring back into shape if it is bent when it is used.

For the bag, 6-ounce drill, heavy muslin, or light canvas is recommended. It may be made as shown in figure 1, D. The four lobes form the rounded bottom of the bag when sewed together. The details of the double-thickness hem as it hangs on the wire loop are shown in figure 1, E. This type of construction is advisable because that part of the bag gets the most Wear. For a lightweight bag, the entire top band may be made of a stout material and the bag sewed to it. The final step is to complete the bag by sewing together the two ends of the material and the margins of the cut lobes.

This beating net is not satisfactory for the capture of moths, butterflies, flies, wasps, and other swift-flying or fragile insects. For them, the nets described in the next three paragraphs are useful.

The general-purpose net should have a loop 12 inches in diameter and a bag of unbleached muslin or of coarse or medium-mesh brussels. It should be tapered more toward the bottom than the beating net, but it should not come to a point. The handle need not be so stout as that for the beating net.

The butterfly net is like the general-purpose net, but the bag is of good-quality marquisette or fine netting, and the handle is a little longer and of lighter weight. This net is also useful in capturing dragonflies and other large-winged insects.

The fly net should have a loop 8 inches in diameter and a bag of medium-mesh brussels or fine netting. The handle should be short and light. The wire loop need not be so heavy as that for the beating net. This net is also good for collecting bees and wasps.

The aquatic net, for collecting insects that live in or on water or on aquatic plants, should not have a circular loop, but should be either square (with the handle attached to one corner) or about semicircular (with the side opposite the handle straight). The bag should be shallow (about as deep as the length of the straight side in the semicircular net) and should be made of heavy scrim with a canvas band for the wire loop.

The bag for any of the nets I have described may be made of silk bolting cloth, which is durable and has meshes of various sizes but is more expensive. Nylon may also be used. The bag for any net, excepting the water net, should be long enough so that the tip may be flipped over the rim of the wire loop to form a pocket from which the netted insects will not escape. Nets should be kept dry. A wet net damages the specimens and dampness causes the fabric to rot quickly. Aquatic nets should be thoroughly dried after use.

A KILLING BOTTLE may be made from any fairly heavy glass jar or vial with a wide mouth. The collector should have several bottles of various sizes (fig. 2, A, B). Empty pickle jars, olive jars, and the like will furnish an assortment of larger bottles. Smaller ones may be made from test tubes or shell vials 1 to 1 1/2 inches in diameter. These should be supplied with tight-fitting corks. Figure 2, C illustrates a convenient adaptation of a screw cap for a jar to keep bees, grasshoppers, and other lively insects from escaping from the killing bottle when it is opened for putting in other specimens. This cap is made by soldering an incomplete metal cone to a screw cap with the top cut out. A metal tube about 1 inch in diameter is then soldered inside the cone.

Calcium cyanide, potassium cyanide, or sodium cyanide may be used as the killing agent in the bottle. Wrap some granular cyanide (a heaping teaspoonful for small bottles, larger amounts for large bottles) in cellucotton, or place it in a "nest" in cellucotton or a little cloth bag, and put this in the bottom of the bottle. Over this place a plug of several layers of cellucotton or a layer of dry sawdust. If the bottle is more than 1 1/2 inches in diameter, a quarter-inch layer of plaster of paris should be poured in and allowed to harden for a few hours before the bottle is corked. If the bottle is a small one, several disks of clean blotting paper, cut to fit the bottle snugly, may be used in place of the plaster of paris.

Cyanide is a deadly poison and should be handled with great care. All bottles should be conspicuously labeled poison and should be kept away from persons who do not realize the deadliness of the chemical. The bottom of a cyanide bottle should be taped so that if the bottle is broken the cyanide will not be scattered about.

To make a killing bottle in which to use ethyl acetate (acetic ether), pour a half inch or more of plaster of paris into the bottom of a suitable jar or vial, allow it to set, and dry it thoroughly in an oven. After the plaster of paris is completely dry, saturate it with ethyl acetate, pouring off any excess fluid. The killing bottle is then ready for use and will last for months if kept tightly corked. When it becomes ineffective it can be dried in the oven and recharged. Insects may be preserved in such bottles for an indefinite time without becoming brittle if they receive an occasional moistening with ethyl acetate. Ethyl acetate is relatively easy to obtain, and the killing bottles have the advantage of being comparatively safe to use.

The killing bottle will last longer and give better results if the following simple rules are observed:

1. Before using the cyanide bottle, put in a few strips of soft paper, such as ordinary toilet paper. This will help keep the bottle dry and will prevent the specimens from mutilating one another. Change these strips whenever they become soiled or slightly moist. Wipe out the bottle if it becomes moist.

2. Keep a special bottle for moths and butterflies. The scales from these insects will stick to other insects and spoil them.

3. Never mix small or delicate insects with large insects like grasshoppers and large beetles. Beetles are hard to kill and must be left in the killing bottle longer than most other insects.

4. Never overload a bottle. Always remove insects from it as soon as they are dead.

5. Discard or recharge bottles that no longer kill quickly. Dispose of the contents of old cyanide bottles by burning or burying.

Many insects should not be killed in a killing bottle but should be placed in 70 percent alcohol or some other fluid. These insects I discuss in more detail later. For them the collector should have a supply of small homeopathic vials of various sizes with corks to fit. He can get them at drug stores.