Robber Flies

Generally they are large, aggressive flies, that tend to have thin and long bodies. There are some exceptions, with a few species having a more rounded appearance and resembling bumblebees.

Robber flies are one of a few predatory fly families that feed on other insects. They tend to perch in an area of their territory, waiting for insects to approach. Once prey is spotted, they attack, using their proboscis to inject a neurotoxin into the prey.

Their ability to paralyze prey allows them to hunt for relatively large insects such as grasshoppers and dragonflies.

Fortunately their aggressive behavior does not extend to humans, making it easy to approach them and watch their behavior.

The first picture shows the Laphria astur robber fly. It is called a mimic fly. Its long thin abdomen resembles a wasp and its hair and coloring resemble a bumblebee.

The physical appearance enables them to approach bees without giving away their predatory intentions.

More than a handful of robber fly genera can be identified by the stripe pattern on the abdomen.

The gold and black abdominal and thoracic stripes on the robber fly in the second picture indicate a species in the genus Callinicus.

Callinus species can often be found at higher elevations along the West Coast.

One of the few robber fly genera to receive a common nickname, the hanging thief (Diogmites), is a fairly common species east of the Rocky Mountains.

The name derives from the fact that in addition to the usual robber fly perching position, they can often it can be found hanging by a couple of legs on a branch, or other support area, consuming their prey.

While a few other robber fly species sport green eyes, the green eyes and brown body serve as typical field identification clues for the approximately two dozen North American species.

© 2006-2011 Patricia A. Michaels