Invertebrates
Robber Fly
Asilidae · also called assassin flies
A robber fly waits motionless on a favoured perch, bristly face angled toward the open air, then launches suddenly to intercept a passing beetle twice its own size. A quick injection of digestive enzymes does the rest, turning a fight it might otherwise lose into a meal it consumes at leisure back on its perch.
Overview
The robber fly, family Asilidae, is an aerial ambush predator found across grassland and forest habitat worldwide. Its enzyme-assisted feeding strategy and ability to overpower prey larger than itself make it one of the more formidable predatory insects in its size class.
Small size, outsized ambition
Where most predators avoid tackling prey larger than themselves, the robber fly routinely does exactly that, relying on precise flight and a chemical shortcut that turns even a much bigger insect into a manageable meal.
Status
Least Concern — widespread and stable across suitable grassland and forest habitat on every continent except Antarctica.
Robber Fly: common questions
How does a robber fly kill prey larger than itself?
A robber fly injects captured prey with saliva containing powerful digestive enzymes that quickly immobilise and begin liquefying the prey's internal tissues, and combined with a strong grip and fast, precise flight used to capture and hold onto struggling prey, this allows the robber fly to subdue insects considerably larger than its own body.
Why does the robber fly have such a bristly face?
A robber fly typically has a distinctive dense tuft of bristles on its face, sometimes described as a beard, which may help protect the fly's sensitive eyes from damage while it grapples with struggling prey during the capture and feeding process.
How does a robber fly hunt?
A robber fly often hunts from a favoured perch, watching for passing insects with notably well-developed eyesight before launching a fast, direct aerial attack to capture prey mid-flight, then typically returning to the same or a nearby perch to consume its catch using its enzyme-assisted feeding method.
Where can you find robber flies?
Robber fly species are found across grassland, forest, and open habitat on every continent except Antarctica, with thousands of described species worldwide, generally wherever suitable perching sites and abundant flying insect prey are available.