Insects should not be killed needlessly. However, when insects are collected for study, killing them is the first step in making a live insect into a scientific specimen.
Freezing and heating. As discussed in sections on jars and bags, and CO2, freezing is a preferred method of killing insect specimens. Most specimens will die over night but some cold resistant insects may require a week or more to die. Kept frozen, specimens do not dry out and can later be processed by pinning and mounting them, eliminating the need for a “relaxing jar” or procedure. Once the specimen is thawed, legs and wings can be moved to position them before letting them dry for display. They will also retain color patterns such as eye colors in horse and deer flies that quickly fade when the specimen dries. Insects can also be killed by heating them above about 135 degrees F, which happens when insect-containing containers are placed on the dash board of a car in the sunlight. However, heated specimens become overactive and will be more likely to injure themselves in the process. It is also cruel!
Killing jar. 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 its main ingredient and can be used rather than specially ordering ethyl acetate (Note: some species like grasshoppers may kick off their hind legs in the process of dying in these poisonous fumes). 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 adhere to the other insects in the jar.
Papered specimens. 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. Dragonflies and damsel flies can also be stored in this manner.
Alcohol. Although alcohols, such as rubbing alcohol or 70% ethyl alcohol (7 parts absolute alcohol in 3 parts distilled water) makes an ideal killing fluid for many (soft-bodied) insect specimens, and is an excellent fluid to store preserved specimens, many soft-bodied insects need to be preserved in a different solution before storage in alcohol-filled vials (see Boiling larvae and KAAD sections). Lower concentrations of alcohol are less effective and some specimens will lose more color or turn black over time when stored in diluted fluid. Alcohol evaporates easily. When storing insects in vials of alcohol, containers must be examined periodically and fluid replenished if needed. Tight seals on caps can reduce evaporation rates.
Boiling larvae and KAAD. 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.
Freeze drying. Larval stages of butterflies and moths can be preserved dry (versus in alcohol after being preserved in boiling water or KAAD) by freeze-drying them in a vaccum. Specimens retain color and hair (setae) patterns better using this method. Special equipment is required, however.