Feather-legged flies are bee mimics, right down to an imitation "pollen basket" on the hind legs, made of a featherlike fringe of hairs. North of Mexico, there are six species in this genus of true flies. In addition to the fringe of hairs on their hind legs, feather-legged flies can be identified by the yellow coloration of their halteres (pair of small, knobby structures that are the modified second pair of wings). Also, males have all-orange abdomens, while females have either dark abdomens or dark-tipped abdomens.
Similar species: The tachinid family, to which feather-legged flies belong, is one of the largest groups of flies and is quite diverse; globally, more than 10,000 species of tachinids have been described, and scientists estimate there are about 10,000 that still have not been described. Most tachinids look something like houseflies, and many, like genus Trichopoda, are bee mimics.
Learn more about this and other tachinid flies on their group page.
Length: ¼ to ¾ inch (varies with species)
Habitat and Conservation
Adult feather-legged flies are usually seen on flowers as they feed on nectar or pollen. Adults may also be observed as they hover around their host species; for example, around melon plants where squash bugs proliferate. Like many harmless insects that have black and orange, yellow, or red coloration, the feather-legged flies' beelike look helps deter would-be predators.
Adults feed on nectar from flowers, but the young are parasitoids of other insects. (A "parasite" usually does not kill its host, while a "parasitoid" usually ends up killing its host.) In this genus, the hosts are usually true bugs, including squash bugs, leaf-footed bugs, plant bugs, shield-backed bugs, and stink bugs.
Feather-legged flies are considered beneficial insects by gardeners. Species Trichopodes pennipes has been used to control squash bugs, which are a major pest of melons, pumpkin, and other members of the squash family.
The female feather-legged fly deposits one or more eggs on a host insect, typically a subadult or adult squash bug, stink bug, or other true bug. Only one of the eggs can survive within the host. Upon hatching, the larva chews into its host's body and consumes its body fluids, without killing the host. Eventually, it grows nearly as large as the host itself. After a few weeks, the tachinid maggot emerges from its host's body, killing it by the trauma. The maggot digs about an inch into the soil and pupates; a few weeks later it emerges as an adult feather-legged fly. There can be 3 broods a year.
People who have experienced the frustration of having legions of squash bugs invade their garden can appreciate feather-legged flies, which are a natural, non-toxic control of those pests. Although parasitized adult bugs will continue to feed, they are usually rendered sterile, and many parasitized nymphs do not survive to become adults.
Nature is a complicated web. Feather-legged flies feed on squash bugs, and squash bugs feed on squash. We eat squash, too, so from our perspective, the squash bugs compete with us for food. Thus the feather-legged flies are our "friends." But the flies need the squash bugs (and other bugs) to survive. From the flies' perspective, our pesticides that kill squash bugs represent a reduction of their food source.