There are relatively few insects that are active as adults in the late fall and winter months, but one of those groups is winter crane flies (Figure 1). There are a number of species of winter crane flies in North America and they are frequently mistaken for other types of flies. They are common in late fall through early spring and may be found under eaves and around porch lights. Occasionally, male winter crane flies are seen flying in swarms in late fall.
Winter crane flies are not true crane flies; they belong to a different insect family. This is a similar situation with velvet ants, as they are not true ants. While they are similar to and closely related to crane flies, winter crane flies have simple eyes (called ocelli) on their head in addition to their compound eyes. They are generally smaller in body size than crane flies and are about 1 ½ to 2 times the size of a common mosquito.
Winter crane flies generally are not of serious economic importance, at least based on reports from Kentucky. This is in contrast to crane flies as there are a few species (such as the European crane fly and those attacking alfalfa in western Kentucky; see KPN article) that can be serious pests. Winter crane fly larvae are reported to develop in decaying organic matter including that of plant, feces, and animal matter. In other regions the larvae have been reported to attack some cruciferous and root crops. They reportedly do not feed as adults.
Ric Bessin, Entomology Extension Specialist