Northern Prairie Wildlife Research Center
Preferred larval fixatives based on alcohol, formaldehyde, and glacial acetic acid are discussed in Stehr (1987). As an alternative, placing larvae into water that has been brought to a rolling boil and removed from the heat will yield excellent specimens. Once the larva is fully distended (after a few seconds to a minute in hot water) it should be transferred to a vial of 70% ethanol. Caterpillars killed simply by immersion in 70% ethanol frequently turn dark, presumably because microbial activity in the gut continues for some period of time. Regardless of the fluid method chosen, the gut contents often leak out over the first few daysit is often desirable to change the ethanol prior to archival storage. Some success may be obtained by placing caterpillars in a self-defrosting freezer for several months. Although much of the color may be preserved in this way, the specimens end up shrunken and inflexible and are not especially useful as study specimens for taxonomic study.
Many caterpillar pigments are lost in fluids. Greens seem to be especially ephemeral in preserved material. The almost immediate color losses that accompany the fluid preservation of loopers can be most disconcerting. Photographs or other types of image-capturing techniques provide the best means of documenting the coloration of living individuals. Preserved collections should be labeled in full with locality, date of collection, and host and cross referenced to any photographs or reared material.