The Science Room Collecting and Preserving Insects

The best insect collecting is often in diverse habitats. A vegetable or flower garden or landscaped facility such as a park, arboretum or zoo will usually have multiple plantings of many different types of plants. But make sure that you have permission to collect first. Note that it is illegal to collect in a federally sponsored facility or national park without a collecting permit. Always be careful not to damage plants when collecting. You shouldn't cause more damage to the plantings than do the pests themselves. Be reasonable and don't hack off side branches, limbs of trees or entire shrubs or flowers unless they are not salvageable (dead or dying). When collecting insects, don't forget to dig in soil. Most plants have a characteristic group of "specialist" insects which feed on them. Other insects may be more general feeders, attacking a large group of plants. Chop into a dying tree or rotting log to discover some interesting specimens.

The basic equipment necessary for field collecting is an insect net, one or more storage boxes, insect nets, pins, pinning blocks, spreading boards, light and pitfall traps, killing jars, killing and preserving chemicals, several vials of assorted sizes, plastic bags and assorted containers. A collecting bag made of canvas, muslin or other strong material is helpful to carry equipment, plant cuttings and insects when out in the field.

The Killing Jar

Insects must be killed before pinning and mounting. Killing jars are used as a sort of "small scale fumigation" to kill collected insects as rapidly as possible, using a liquid fumigant or killing agent (ethyl acetate/nail polish remover) that produces a toxic atmosphere that the insect cannot breath.

When placed in the killing jar, insects often close their spiracles, but eventually they must open them. The process may take several minutes for smaller insects or up to a half hour or more for larger specimens. Because large, hard-bodied insects such as beetles die slowly and may damage other insects placed in the same killing jar, you may need more than one jar.

In the bottom of each jar, place about 1 to 1 1/2 inches of absorbent material, such as cotton, shredded newspaper, Plaster of Paris or wood fiber (sawdust). If Plaster of Paris is used, pour it about 1 inch deep and allow it to dry for at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard circle just slightly larger than the inside diameter of the jar and push it into the opening against the plaster in the bottom. Wrap the outside bottom third of each jar with masking tape to prevent cuts in case the jar is broken. Attach a label that says POISON.

The killing jar is now ready to charge with a killing agent. Pour enough ethyl acetate (a tablespoon or so) into the killing jar to thoroughly wet the dry, absorbent plaster. Use a bit more if the plaster will absorb it. Pour off any excess into the original container. Do not use too much or you may "wet" and damage insects that you collect. Turn the lid on tightly to prevent loss of fumes. As the killing jar is used, it will lose its strength so the killing agent must be replenished from time to time. Tear up some strips of paper, crumple them slightly and place them in each jar. This will help to prevent insects from damaging one another.

Pinching the thorax of large butterflies or moths before placing them in the killing jar will prevent them from flopping around and damaging the wings. Squeeze them for 20-30 seconds between thumb and index finger and put them in the killing jar. This procedure stuns the insects so they do not flutter once inside the jar. Remove butterflies and moths from the killing jar fairly soon so their wings do not become soaked with killing agent.

The Relaxing Jar

While insects should be pinned on the same day they were collected, this is not always possible. So before pinning these specimens left in the killing jar too long, to restore their flexibility, it is necessary to "relax" them. By placing them in a relaxing jar at high humidity for a few days we can restore their flexibility enough to allow pinning without damage to the specimens.

Relaxing is always a risky process and, if carelessly done, the specimens may be ruined. A relaxing jar is easy to make. Simply use another baby food or larger jar as the relaxer. Place some absorbent material such as newspaper, sand or cotton in the bottom and cut a blotting paper disk to fit tightly inside. Moisten the material with water and add a drop or two of ethyl acetate, phenol, Lysol or laundry beach (Hi-Lex, Purex, Clorox) to prevent mold. Place insects on the paper, close the jar tightly and let it sit for about 2-3 days. Check the jar. If the insects are flexible, mount them immediately. If the specimens are still too stiff, keep them in the relaxer for a few more days, but watch them carefully. Insects will mold and decompose if held in the relaxer too long.

The Collecting Net

Aerial nets for collecting flying insects can be ordered or made at home from a 4-foot length of doweling, about 4 feet of heavy wire and a half yard or so of sheer nylon or orlon netting. Grooves are cut across one end of the handle, then a one-half inch deep hole is bored on one side of the handle (in the groove) three inches from the end. A second hole is bored one-half inch deep in the opposite groove four inches from the end. A four foot length of heavy wire is bent into a hoop and attached to the handle by a 4-inch aluminum slip collar, which holds the wire hoop in place. The bag, once hemmed and attached to the hoop, is about one foot in diameter, two to three feet long and tapered to a point. The bag is slipped onto the wire hoop before it is attached to the handle. A muslin or denim band is usually sewn over the hoop end of the bag to make the net last longer.

Sweeping or beating nets are made like aerial nets. However, the net bag is constructed of strong muslin material instead of the lighter netting. These heavier duty nets are used to collect insects from grass, trees and shrubs by swinging the net through heavy foliage. Thus, these nets are sometimes referred to as "beating" or "sweeping" nets. The sweeping net is widely used to sample insect populations in standing field crops such as alfalfa, wheat and soybeans. As the surveyor walks through the crop, the net is swung in an arc a specified number of times - e.g. 10, 20, 50, 100, etc. Done at several locations over time in a field, and the results totaled, a reasonable assessment of the pest population can be made, compared with economic thresholds and management/control decisions made.

The Aspirator

An aspirator is a suction device for collecting small insects which are difficult (or hazardous) to capture with the fingers or with an insect net. Basically, it consists of a large glass or plastic vial, a length of flexible rubber tubing, some rigid plastic or metal tubing and a rubber stopper with 2 holes cut in it to receiving the tubing. A small piece of cheesecloth or fine metal screen serves to seal the suction tube on the inside so that insects are not sucked into the mouth. Bear in mind that if you collect ants, you may not suck the ants through the fine mesh, but their defensive secretion (formic acid) can give you a nasty mouthful, especially if the ants are large and numerous.

To make an aspirator, bend the two lengths of rigid tubing and fit the tubes into a rubber stopper. The long tube should extend down to within about one inch of the bottom of the vial when it is in proper position. Attach the small piece of cheesecloth or metal screen to the short piece of tubing with solder, glue or a rubber band. (This is to prevent you from sucking several bugs or bits of dirt into your mouth when you are using the aspirator.) Now attach the rubber tube to the short piece of rigid tubing.

To use the device, just place the long tube beside a small insect, put the rubber tube into your mouth and suck sharply. With a bit of practice, you will find that this is an excellent way to collect smaller insects with ease.

Light Traps

Many types of insects are attracted to light and can be captured there by hand. A light trap offers the advantage that it will continue to trap specimens without being constantly watched by the collector. Insects are quite sensitive to different types of light; therefore, more of certain types can be captured with "black" (or ultraviolet) light as opposed to the regular "white" light given off by most standard light bulbs. The difference in attractiveness of the two types of light is due to the wave lengths produced by the two kinds of bulbs. Black light consists mainly of the shorter wave lengths which are more attractive to night-flying moths, flies and beetles. White light bulbs (producing mostly longer wave lengths) attract some moths and other insects, but not as many as a black light. Simply turning your home entry lights on or standing under a street light or in your car headlights often produces many specimens, including many horticultural pest insects. Many of the night-flying cutworm moths can be captured when feeding on various flowers during evening hours.

All that is needed to make a simple light trap is a battery-operated lantern or an automobile trouble light with a 100-watt or larger bulb, a large metal funnel (you can also make one of plastic sheeting, but remember this is flammable) and a wide mouth jar or a large tin fruit juice can. Hang the light outdoors away from the buildings, in a sheltered place, near a power source, if needed and no more than 4 feet off the ground. Construct a wire framework to support the lantern or suspended bulb, funnel and trap can. Make sure that the end of the collecting funnel is large enough to allow larger insects to pass through. Place some crumpled newspaper in the bottom of the can (about 2 inches deep) and lightly wet it with killing solution. Start the trap at dusk and empty it in the morning. A simpler trap setup is to prop up a white sheet to serve as a reflecting surface, then to sit a lantern in front of it on a chair or stool. Collect the insects attracted to the sheet as they land on the surface. Blacklights are made in the same form as regular fluorescent tube lights and can be operated in similar types of fixtures. Do not look directly at the blacklight bulb, because ultraviolet light can damage eyes. Night-flying insects seem to be more often attracted to light traps placed in sheltered areas (i.e. protected from wind by trees) than those in more open areas.

Pitfall Trap

A pitfall trap will catch many ground beetles and other insects that live on or in the soil. It consists of a trap can that is buried in the soil, level with the rim so that insects attracted to it will fall in. Once inside, it is difficult for them to get out. An attractive bait in the bottom will increase the drawing power of the trap. Use pieces of spoiled fruit, vegetables, excrement or meat. Cover the trap with a board placed on small stones so insects can crawl under it and into the can. This arrangement will protect the trap from wind and rain, but allow access to the insects you want to catch. It will also help to hold insects inside the trap once they are caught. Remove the insects that you catch each morning.

Preserving Insects

  • Soft-Bodied Insects - Many types of insects, including aphids, springtails, thrips, mayflies or silverfish, are soft-bodied and cannot be pinned successfully. The same is true of many immature insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most soft-bodied insects will shrivel or decompose. Such insects must be preserved in liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied specimens for the long term, their color must be "fixed" or they may fade in some cases or blacken in others. The "fixing" process prevents, reduces or delays color change.

    For the long term, insects are preserved in ethyl alcohol, usually of about 70 percent concentration (70% alcohol, 30% water). Isopropyl alcohol can also be used, but with less success. Over time, stronger alcohol solutions can cause colors of specimens to darken and bodies to shrivel. These problems can be largely prevented in either of two ways. The best way is to "fix" the insect tissues and color by killing the specimens in boiling water. For smaller specimens, simply dip them in boiling water for about 30 seconds and then transfer them to 70 percent alcohol. Use more extended periods for large-bodied insects.

  • Hard-Bodied Insects - Since insects have a hard shell or exoskeleton and all of the soft parts are on the inside, they tend to keep rather well after drying, even for long periods of time. Only a small amount of maintenance is necessary to keep them in good condition. Many specimens in museums today are over one hundred years old and look just as they did on the day they were collected. Certain types of insects may fade, but others hold their colors indefinitely. If you want to study insects in the winter, you must work with collections of dead insects or with living laboratory-reared material. Remember that dead, pinned insects are very brittle and delicate. They must be handled very carefully and never jarred, dropped or touched directly. Specimens whose legs, antennae and wings are broken and lost are essentially worthless.
Pinning, Mounting, and Displaying Insects

Insect Pins

Special pins are needed to pin insects. These pins are longer, stronger, and thinner than an average pin. They come in several sizes from 00 through 7, the size of the pin increasing with each number (2's and 3's are most useful). Insect pins are purchased from biological supply houses and some hobby stores, in packs of 100. Never use common pins.

Most adult insects may be pinned directly through the thorax if the pin is not too large and does not distort or destroy it. Fragile or tiny insects (such as mosquitoes) which are too small for a pin will need to be glued to the point of a small triangular paper punch-out which has already been stuck through with a pin.

Different groups of insects require different pin placement. With most Orders, the pin should pass through the middle of the thorax such that the specimen appears balanced in relation to the placement of the pin. The insect's body should be perpendicular to the pin. In bees, wasps and flies (Hymenoptera and Diptera) the pin should pass between the bases of the forewings, just to the right of the middle. In beetles (Coleoptera) the pin should pass down through the right outer wing. In the Hemiptera and Homoptera, the pin should pass through the triangular scutellum slightly to the right. With grasshoppers and crickets (Orthoptera) pin through the thorax to the right of the middle line. In butterflies, moths, and dragonflies (Lepidoptera and Odonata), the pin goes through the center of the thorax and the wings should be spread properly. Consider visibility, breakage, and space when positioning legs and antennae. Once your insects are mounted and allowed to dry they are very fragile.

Spreading Board

Mounting butterflies and moths is a special technique that requires a spreading board to do an attractive job. The spreading board is usually made of soft pine with a piece of balsa or cork underneath the center groove to receive insect pins.

When pinning and spreading a butterfly or moth, before you begin to work, cut several thin strips of paper about 1/4 inch wide and 8-10 inches long. Once these are ready, pick up the insect by the thorax and carefully push a pin through the middle of the thorax. Adjust the position of the butterfly on the pin and make sure that it is level, both on the sides and in both front and back.

Place the pin into the hole in the tallest step of the pinning block, being careful not to damage the fragile wings. Adjust the width of the groove in the spreading board to be just slightly wider than the body of the butterfly. Remove the pinned insect from the pinning block and push the pin into the slot of your spreading board until the bases of the wings are just level with the top of the two side pieces.

Slip a paper strip between the wings (if they are upright) and use it to force the wings on one side down into position. Pin the ends of the paper down to hold the wings loosely in place. Do the same with the wings on the other side, also pinning the ends of the paper down.

Now take another insect pin or needle and slip the point through the leading edge of the right forewing (there is a strong vein just at the front edge of each wing) near its attachment to the thorax. Be careful not to tear the wing. Loosen the forward end of the paper strip and gradually bring the forewing up into final position. Pin the wing down with a paper strip. Repeat this procedure with the forewing on the other side. Using the same technique bring both hindwings into proper position and fasten all four wings firmly with the paper strips.

Note carefully that the rear edge of the two forewings should make a perfectly straight line across the back. The hindwings should be pinned so that the rear edge is held just slightly away from the abdomen. Position antennae with pins and if the abdomen has drooped, prop it up with pins so that it dries in a natural position.

Allow specimens to dry for several days before you remove the pins. Drying "freezes" the wing muscles of the insect in position. Rushing the drying process somewhat by placing specimens in an oven at 125 oF for about an hour will work, but may result in the wingtips curling upward and spoiling the insect's appearance. Be very careful if you attempt this. Using wider (3/4 inch) paper strips to hold the wings down will help to prevent distortion.

Large-bodied moths like Cecropia should be cut open on the underside of the abdomen and the contents removed with a cotton swab. The body cavity should be filled with cotton so that the specimen looks natural from above. If this is not done, the fatty material in the abdomen will decompose, releasing oils which may discolor and ruin the specimen.

Pinning Blocks

First, place the pin in the insect thorax in the proper position on the top step of the pinning block, pushing it in so that the top of the insect is quite close to the pin head. Then, remove the pin from the top step, reverse it and place the head of the pin in the lowest step of the pinning block. Push it down as far as it will go. This will result in positioning each insect about one-fourth inch from the pin head. The middle step on the block is to position the collection label. The lowest step is used to position the insect identification label.

Labeling Insects

A collection has little value unless each insect is properly and accurately labeled. Labeling must be done as soon as possible after collecting, pinning and mounting or vital information may be lost. Note that many insects in museums today stand as living documents of biological diversity. Their precise collection locations, habitats, and data on plants on which they were found is important documentation. Many of these habitats have been or are being altered and in some cases destroyed. Many plant and animal species, once common and together in biological ecosystems, are now endangered or in some cases are already gone. It is essential that the presence of insects, plants and other creatures be documented for future generations.

Labels should be as small as is reasonable, and no larger than 1/2 inch wide by 1 inch long. Labels should be made on a computer and printed. Trim labels with a sharp paper cutter so the edges make nice, clean, and flat rectangles. Two labels should be placed on the pin below each insect specimen. Both labels should be of the same size and lined up parallel to the length of the body of the insect (not cross-wise). The insect head should be at the left and the label should read from left to right.

  • The top label (collection label) should have the county and state in which the insect was collected, the collection date and the name of the collector.
     
  • The lower label (order label) should show the Order name of the insect.
     
  • Many entomologists place another label between the collection label and the order label which gives the host plant, habitat or other pertinent information, however, this label is not required.