Robber Fly Bizarre

Explanation: Bizarre and startling is this insect I encountered in the forests on the slopes of Mt. Kenya in eastern Africa. Looking like an alien invader, this is an Old World species of robber fly.

Robber flies are swift-moving members of Order Diptera, the flies we love and hate. Robber flies are particularly adapted to be ambush and active predators of insects and spiders, in both their adult and larval forms.

Robber flies have what are called haustellate mouth parts, adapted for sucking instead of chewing. They have an elongated proboscis or beak through which they suck the body juices of their prey after piercing it with a sharp mouth part called the hypopharynx.

Although robber flies seldom bite people, their bite can be quite painful, so I decided not to handle this particularly hazardous-appearing specimen. Robber flies can be very aggressive and take on horse flies and are known to attack wasps, bees, dragonflies, grasshoppers, and other flies.

This particular subfamily of robber fly, the Laphriinae, has a number of species, some of which are bumble bee mimics. They lay their eggs in rotting wood.

I can find no ecological studies of this particular robber fly, of genus Proagonistes, nor do I know what species this is beyond the genus level. The larvae of many species of robber flies remain unknown, and adult forms of many species are unstudied.

Acknowledgments:
My thanks to entomologists Dennis Paulson, Rob Cannings, and Eric Fisher for the identification.

Information:
According to entomologist Eric Fisher, this genus of robber fly, Proagonistes, is a relative of the genus Andrenosoma, endemic to Africa, and it won't key out in available (albeit obsolete) literature.
General source information:
Borror, D. J., D. M. DeLong, and C. A. Triplehorn. 1976. An introduction to the study of insects. Fourth edition. Holt, Rinehart and Winston, New York. 852 pp.

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