You are here

Prairie Robber Fly

Prairie Robber Fly
Diogmites angustipennis
(Order Diptera; Family Asilidae)

Diogmites angustipennis (photo by Amy Coffman)
(Kansas: Sedgwick County. Private property, 37°48’40.62”N, 97°19’11.52”W. On wooden gate. 6 September 2011).

Adult Diagnosis:  This common Kansas insect is velvety reddish-brown with black eyes (although sometimes greenish), proboscis, tarsi and body bristles.  The body bristles are found on the thorax and legs while the face is bare.  The body measures around 25 mm in length with 4 to 5 black, bar-like spots on the lateral edges of the abdomen.  A claw-like spur is found on the front tibia.  The palpi are two-segmented, and there is a characteristic depression between the two compound eyes.

Adult Natural History: Generally, little difference between the sexes is observable aside from the genitalia.  Females can be larger than the males and often have wide abdomens.  Young overwinter as larva before the pupal stage which lasts two to six weeks.

Prairie robber flies are most active during the warmest parts of the day when they hunt in sunny, open areas.  Their activity is greatly reduced or halted during overcast weather conditions.  They preferentially perch in sunlit areas where they wait for prey.

Males exhibit courtship behavior, and mating generally occurs tail to tail. 

Female robber fly ovipositing (from:

Distribution:  This late-summer species is common across the mid to south central US, as well as Idaho, Utah, and South Carolina.

PRF distribution (from:

Habitat:  Most robber flies are found in dry, open habitats such as prairies, glades, savannas and woodlands.  Larvae spend their time near the soil in decaying stumps or logs, or next to plant roots.

Diet:  Prairie robber flies are highly predaceous, feeding on other insects, such as honey bees and wasps.  They will lie in wait on bare areas of soil, rest on the tops of dead weeds and bushes, or perch on stones or logs.  They often hang from stems or branches while feeding and will inject the prey with paralyzing saliva, and the resulting liquefied contents of the prey are sucked up through the proboscis.  Larvae are ectoparasites or predators that feed on other insects’ eggs, larvae or pupae.

Prairie robber fly feeding (from:


Conservation Status: Under concern


Robber Fly



Bug Guide: Species Diogmites angustipennis – Prairie Robber Fly

Geller-Grim: Robber Flies:

Nature Watch –Robber Flies (Insecta: Diptera: Asilidae):


Barnes, J. K., N. Lavers, and H. Raney. 2007. Robber flies (Diptera: Asilidae) of Arkansas, U.S.A.: notes and a checklist. Entomological News 118: 241-258.

McCravy, K. W., and K. A. Baxa. 2011. Diversity, season activity, and habitat associations of robber flies (Diptera: Asilidae) in west-central Illionis. American Midland Naturalist 166: 88-97.

Salsbury, G. A., and S. C. White. 2000. Insects in Kansas. Kansas Department of Agriculture, KS.

Submitted by: Amy Coffman, November 2011

Wichita State University
Generated on 2011. This website is continuously updated.
Comments can be sent to Mary Liz Jameson.
Designed by Bioadventures.