Hanging Thief Robber Fly

Diogmites neoternatus — the hanging thief robber fly — is one of about 7,000 species in family Asilidae (the robber flies — one of the most ecologically diverse families of predatory flies on Earth) and one of about 75 species in genus Diogmites. The species is widespread across the eastern and central US from southern Canada south through the eastern US to Mexico. Adults are 18-25 mm long, slender, with the typical robber fly body plan: long legs, large compound eyes with depressed center (the 'hollow' between the eyes is a diagnostic asilid feature), powerful wing musculature for aerial predation, and sharp piercing mouthparts. The species is distinguished by the unique 'HANGING' FEEDING POSTURE that gives the species its common name. Most robber flies feed on captured prey while perched normally on a twig or leaf, with all six legs holding the perch. Hanging thief robber flies (genus Diogmites) instead HANG SUSPENDED FROM A SINGLE FRONT LEG attached to a perch (typically a twig, grass stem, or other slender vertical structure), with the other legs free to grasp and manipulate the captured prey item during consumption. The hanging posture allows the robber fly to handle large prey items (proportionally larger than the predator's own body weight) without the burden of supporting the prey on the substrate. The hanging posture is unique among robber flies and is one of the most-cited examples of unusual feeding biomechanics in Diptera. Hanging thief robber flies are EXCEPTIONAL AERIAL PREDATORS — they perch on prominent waterside or meadow substrates and watch for passing flying prey; when prey is detected, the robber fly launches into a high-speed pursuit flight and CAPTURES THE PREY IN MID-AIR using the long legs as a basket. Documented prey include large bees (including honey bees and large bumblebees), wasps (including yellowjackets, paper wasps, and even larger wasps), dragonflies, large flies (including other robber flies — robber flies are notorious cannibals), and occasional smaller moths and butterflies. The species is one of the few aerial insect predators that can subdue large bees and wasps despite the prey's defensive sting (the robber fly's sharp piercing mouthparts can disable the prey's stinger before being deployed). Once the prey is captured, the robber fly carries it to a perch (using the hanging posture) and stabs it with sharp piercing mouthparts, injecting digestive enzymes that liquefy the prey's internal tissues for sucking consumption. The species is harmless to humans (rarely bites, the bite is medically insignificant) and is a major beneficial generalist predator in eastern NA grasslands and woodland edges.