A robber fly, (Diptera: Asilidae). Photo by Drees.
Common Name: Robber fly
Scientific Name: Varies
Order: Diptera
Description: Adult stages are medium to large (3/8 to 1-1/8 inch) flies often observed on stems of plants, on the ground or flying low. Species vary in appearance and some mimic wasps and bees. Most species are gray to black, hairy-bodied, have a long, narrow, tapering abdomen containing segments that may be banded, patterned or contrasting in color. The heads of adults have a depression between the eyes when viewed from the front. They have long, strong legs for grabbing prey.
Some robber flies resemble bees in a appearance but can readily be separated since true flies have only one pair of wings. However, bee flies (Diptera: Bombyliidae) are another family of flies, and include many species of stout-bodied, yellow haired flies often seen hovering or resting on the ground or on flowers in open, sunny areas. Many have wings marked with darker patterns and they hold their wings outstretched. Larvae are
A robber fly, Laphria sp. (Diptera: Asilidae). Photo by Drees.
parasitic on immature stages of other insects including Coleoptera, Diptera, Hymenoptera, Lepidoptera, Neuroptera and Orthoptera.
Life Cycle: Adults lay eggs in the soil or in plants. Eggs hatch into slender, shiny, white, legless larvae that develop through several stages before pupating. The life cycle usually requires more than one year to complete.
Habitat and Food Source(s): Adults have piercing-sucking mouthparts. Adult robber flies perch on stems of low plants or other objects and attack prey in the air. They feed on bees, beetles, dragonflies, other flies, grasshoppers, leafhoppers, wasps, and other insects. Larvae live in the soil, in wood and other habitats, feeding on organic matter, other arthropods such as white grubs, beetle pupae and grasshopper egg masses, and they may be carnivorous.
Pest Status: Adults prey on a variety of arthropods; considered to be beneficial insects, except for those that feed on bees and other beneficial insects; adults, handled improperly, are capable of inflicting a painful bite.
A bee fly (Diptera: Bombyliidae). Photo by Drees.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: Borror et al. 1989; Oldroyd 1964. Swan & Papp 1972.