Collecting and Preserving Insects
Making an insect collection is one of the best methods of learning about insects. In the process of locating, handling, and preserving insects many observations about the life cycle, habitat, behavior and appearance of insects are naturally made. These observations contribute greatly to understanding insects and their relationships and roles of insects in the environment.
Insect collections are necessary for identification of insects. Proper identification of insects is a necessary step to properly communicate any information about insects. It is essential that good identifications are made so scientists report their findings properly. Without good identifications, scientific studies become of little value. An insect collections can also be an item of beauty. A well preserved and neatly presented collection can make an attractive display in a home or office. Displays of insects usually become a conversation piece anywhere they are on display.
Killing Insects. Insects should not be killed needlessly. However, when insects are collected for study, killing them usually becomes a necessary step to acquiring a complete, quality specimen. Perhaps the easiest method to kill an insect is simply to put it in a freezer. Most specimens will die over night but some cold resistant insects may require a week or more to die. Usually in field work, insects are collected into a killing jar. Killing jars may be in any size but seldom need to be larger than a pint. Select a jar with a tight fitting lid. Killing jars can be made simply by adding a few strips of paper towels to a jar and then adding a few drops of ethyl acetate. Most nail polish remover has ethyl acetate as an ingredient and can be used rather than special ordering ethyl acetate. The paper allows insects in the jar to keep separated and also picks up excess moisture. More permanent killing jars are made with a layer of vermiculite topped with a layer of plaster of Paris (mixed with water) then allowed to dry. The exterior of the bottom of the jar can be covered with fiber tape or duct tape for additional support. Label the jar clearly with a poison notice.
Avoid putting moths in the same killing jar with other insects. It is best to keep a separate jar for this group because scales from the wings rub off easily and will coat the other insects in the jar. Butterflies can be immobilized or killed while in the aerial net. Grab and squeeze the specimen by the thorax between the thumb and forefinger with the wings folded over the back. The butterfly will be stunned or killed, depending on force of squeezing and time. Thereafter, specimens can be slipped into a glassine envelope or paper “triangle” (see description below). Specimens can be stored in this manner or mounted, either directly or after “relaxing” the specimen.
Soft bodied insects may be collected (and preserved) in alcohol. Ethyl alcohol or rubbing alcohol (70%) are fine for this purpose. Many insects, especially caterpillars, lose their color when preserved directly in alcohol. To improve the appearance of these insects they may be killed in boiling water for a few seconds or first killed in a solution called KAAD (available from a source of entomological supplies). KAAD consists of a solution of: 1 part kerosene, 7-10 parts 95% ethyl alcohol, 2 parts glacial acetic acid and 1 part dioxane.
Preserving Insects. Most insects have a sufficiently hardened exoskeleton to allow them to maintain their shape after they die. Basically, the hardened exoskeleton remains and the soft internal structures dry up. Insects are stored on insect pins, glued to cardboard points, in alcohol, in envelopes or on microscope slides. Most insects are pinned through the thorax on the right side. Butterflies, moths, dragonflies and damselflies (Lepidopera and Odonata) are often pinned through the center of the pronotum. Select good quality insect pins which are longer than sewing pins and are made of materials to resist rust. Insect pins are available from biological supply houses. Number 2 or 3 pins are the most commonly used for insect collections. Thinner or thicker pins have special purposes.
When preserving insects consider that the characteristic body parts should be preserved and observable after they are preserved. A knowledge of the insect group may be necessary to know the specific methods used to preserve a group of insects. Usually it is wise to position legs and wings in a manner to help preserve them by folding them out of the way. Also specimens should be positioned to made good use of space in the collection. Insects should also be positioned on the insect pins at consistent heights. Use a pinning block to be standardize the height. Small specimens, too small to pin directly, can be mounted on small cardboard points. Points are small cardboard triangles and a point punch can be purchased to make them consistently and in quantity. Two ply bristle board can be used for pins and labels although index cards make a reasonable substitute. White glue (like Elmer’s) is used to glue small insects to points and also to repair damaged specimens. This glue is water soluble and can be soaked in water to reposition the specimen later.
Butterflies, moths, dragonflies, damselflies and a few other groups of insects are sometimes preserved in glassine envelopes or paper triangles. These insects can be laid flat and the envelopes help hold the delicate body parts which may break off. This method allows a large number of specimens to be maintained in a little space. However, examination of the specimens is not as convenient as with pinned specimens. These same insects are often prepared with the wings spread out for easy viewing. A spreading board is needed to spread the wings and hold them in position while they dry. Drying may take a week or more depending on the environmental conditions. Once dry the wings will remain outstretched unless there is too much moisture.
Regardless of the preservation method, all insect specimens should be carefully labeled with information about when and where it was collected. Information on the labels is valuable from a scientific standpoint. Small, neatly printed labels of a consistent size really adds to the attraction of an insect collection. Labels should have information about the country, state, county, nearest town, collecting date , and collectors name. Additional information about the collecting method or host plant are also useful. A second label with the scientific name is usually added below the collection label. Keep the height of the labels consistent by using a pinning block. Labels should be placed on the pin with the insect, inserted in the alcohol vial, or written directly on the envelope.
Collecting Insects. Insects can be found in nearly any habitat. Sometimes they are very obvious but other times it is necessary to do some hard work or careful observation to discover them. It is important to visit a variety of habitats to collect a wide variety of insects. Be sure to look around lights, under logs or boards, in grassy fields, near ponds or streams, and on flowers which are all productive locations for insect collecting. Most insects are active in the spring, so concentrate you effort at that time of year. However, grasshoppers, stinkbugs and other insects may not mature until later in the fall of the year. Therefore, it is necessary to collect in the fall to acquire adult specimens of some of these insects.
Capturing insects for observation or to preserve them in a collection is sometimes quite easy but make be a physical challenge for some types of insects. Collecting a specific insect or group of insects requires special skills and patience. The most important piece of collecting equipment is the jar. Many insects can simply be knocked into an open jar and the lid closed quickly. Forceps are also useful to pick up small or hazardous insects. A soft forceps is preferred for most field use because it is less likely to damage soft specimens.
Perhaps insects nets are the most recognized piece of insect collecting equipment. The typical net is an aerial or butterfly net. However, aerial nets are best used by dropping them over a resting insect or by scoping an insect from a resting site on a plant. Running across a field with a net overhead and swinging wildly to catch a flying insect is very inefficient and typically results in a broken specimen. A sweep net has a heavy frame and a heavy cloth bag. It is used by brushing the net bag back and forth (somewhat like a broom) with the net bag in foliage like grass and flowers. The sweep net motion should flip the bottom of the bag around at the end of each stroke into position to make the next stroke through the foliage. The number of “sweeps” can be just a few to 100 or more to amass a large number of specimens in a short time. It is not a very good method to collect delicate specimens because many will be broken in the thrashing of the net.
Another useful tool is the beating sheet. This is simply a piece of heavy cloth held flat by sticks usually in an X fashion attached to the sheet corners. The beating sheet is held or laid under trees or shrubs and the foliage above is beaten with a heavy stick or simply shaken. This action dislodges many insects that fall onto the sheet. Once on the sheet the insects can be viewed, sorted or collected in a jar.
Aquatic nets are extra heavy and often have a flat side giving the net bag a D shape or triangle shape. These nets are used by placing the net bag on the bottom of a flowing stream. Insects are dislodged upstream by rubbing rocks on the bottom or kicking up the bottom of the stream. Dislodged insects them accumulate in the net.
Insects traps can be purchased or made, often fashioned with common household items such as plastic milk jugs or soda bottles. Traps are also very effective for collecting insects. Traps can be passive or include an attraction to insects like bait or light. Lights are very effective at attracting insects of many types. Black lights and mercury vapor lights are used and sometimes in combination. A simple white sheet with a black light shining on it can be very effectively used to attract insects. Passive traps are designed to intercept insects as they pass by. Window pain traps consist of a pain of glass with a trough below that is filled with liquid to collect the insects that fall. Liquids in these traps can be salt water, soapy water or ethylene glycol. Ethylene glycol should not be used if wildlife or pets may have access to the liquid. Pit fall traps are placed in the ground flush with the surface. Insects simply fall into the traps when they walk. Pit fall traps are very useful to collect crawling insects that are active on the ground at night. Malaise traps are sheets of netting held vertically with a tent like cover on the top. At the upper corners of the tent cover are a funnel and a jar which can be changed periodically. Malaise traps and window pain traps collect many types of insects.
Baits should be selected or made to attract the specific insects of interest. Sugar baits consist of a mixture of brown sugar, yeast, overripe fruit such as bananas or peaches. Sugar baits are allowed to ferment for a few days and then they are used in a trap or simply painted on the side of a tree. Many moths, beetles, and other insects are attracted to the sugar baits where they can be collected easily. Other insects are attracted to dung or decaying meat which can also be used as a bait. Pheromones are chemicals that are given off by an insect to affect behavior of other members of the same species. There are pheromones for alarm and aggregation. However, for traps the most effective pheromones are sex lures. Sex pheromones are chemicals given off by a female to attract males of the same species for mating. There are several hundred sex pheromones that are available commercially.
A Berlese funnel is a good tool to collect small insects from leaf litter, plant debris or old logs. A Barleys funnel consists off a funnel with a coarse screen on the inside and a dish of alcohol below to catch the insects as they move out of the plant material. The plant material can be allowed to dry or force dried using a light bulb or other heat source to drive the insects out. Simple Barleys funnels can be home-made using plastic soda bottles by cutting off the bottom and inserting a piece of screen.
Storing an Insect Collection. Insect collections can be maintained in almost any box large enough and deep enough to hold the pinned insects. Cigar boxes with styrofoam or cork layer on the inside bottom are useful. More permanent boxes are Schmitt boxes or Cornell drawers which can be purchased commercially. Schmitt boxes typically have a pinning bottom and a closed hinged lid. Cornell drawers have a glass top and smaller boxes called unit trays are used to fill the box and hold the specimens. Stored insects are susceptible to attack by small dermestid beetles (Coleoptera), book lice (Psocoptera) and sometimes ants or other pests. It is necessary to use naphthalene as a repellent, paradichlorobenzene as a fumigant or a regiment of periodic cold treatment to maintain a collection free of dermestid beetles. However, these chemicals may react with styrofoam. Pesticide strips containing DDVP or dichlorvos are also available from suppliers of entomological supplies to protect insect collections from these pests.
References
Borror, Triplehorn and Johnson. An Introduction to the Study of Insects. Godwin, W. 1996. Making and Insect Collection, (http://insects.tamu.edu/links/collect1.html) Jackman, J. A. 1996. 4-H Entomology Guide, Study Materials for 4-H Entomology Contest. Texas Agric. Extension Service. Peterson, A. 1962. Larvae of Insects, An Introduction to Nearctic Species. Columbus, Ohio.