Is it a dragonfly? Is it a wasp? Nope, it’s a robber fly. Robber flies are predatory insects in the Asilidae family. Arkansas is home to several species of robber flies ranging in size from 3mm up to two inches (5.08 cm if you want to keep it in the metric system). The species pictured is Promachus rufipes, common name red footed cannibalfly, which measures about 4cm long. Another name for this species is bee panther. A perfect nickname judging by the picture.
Large, fierce and just flat-out cool looking, the red footed cannibalfly’s body shape reminds me of an attack helicopter. And just like attack helicopters they are fearsome. Size of prey is no deterrent. Adult cannibalflies attack wasps, bees, dragonflies, grasshoppers, other flies, spiders and even hummingbirds. They intercept many soon to be meals in mid-air by grasping them with those bristly legs, then, using a sharp proboscis, the fly injects a venomous cocktail of nerve toxins and digestive enzymes. Prey is quickly immobilized and digestion by the robber fly has started. The fly then finds a quiet perch, usually a sunny spot like in the photo, and slurps the liquefied innards through that proboscis much the same as you slurp a chocolate milkshake through a straw.
The larval stage of robber flies are worm-like but voracious predators, too. They live in soil, rotting stumps and other moist organic material, but due to a secretive and solitary life have been much harder to study.
Robber flies are closely related to horseflies, and though they don’t feed on blood, they can deliver a painful bite. My introduction to a robber fly, which I believe was in fact a cannibalfly, came when I was around 8-years-old in the form of a nip on the leg and resulted in a revenge smashing of the devilish looking insect with a fly swatter when it landed on the porch swing after biting me. Bites on humans are rare, though, and besides the pain are harmless.
Robber flies are supreme predators in the insect world, and though vicious play an important role in ecological balance.