Asilidae

Definition

A large, cosmopolitan family of predatory flies (order Diptera) commonly known as robber flies or assassin flies. Members are characterized by a robust, often hairy body, large compound eyes, strong legs adapted for seizing prey in flight, and a stout, piercing proboscis used to subdue and consume other insects. Adults are active aerial predators that typically perch in open, sunlit habitats and ambush passing prey, including bees, wasps, dragonflies, and other flies. The family comprises roughly 7,000 described species in more than 500 genera, making it one of the most diverse families of Brachycera.

Etymology

From the type genus Asilus (Latin asilus, a gadfly or horsefly) + family suffix -idae.

Example

A large Asilidae such as Promachus hinei may capture and subdue a foraging bumblebee mid-flight, then perch to consume the liquefied contents through its proboscis while the prey is still grasped in its raptorial forelegs.

Synonyms

• Robber flies
• assassin flies

Related Terms

• Diptera
• Brachycera
• Asiloidea
• raptorial legs
• Proboscis
• predatory behavior
• mimicry
• Stenopogoninae
• Laphriinae

Usage Notes

The common name 'robber fly' emphasizes their ambush-hunting strategy; 'assassin fly' highlights their lethality to other insects. Asilidae are frequently Batesian mimics of bees and wasps (e.g., genus Mallophora), which can lead to misidentification. The family is morphologically diverse, with some subfamilies (e.g., Leptogastrinae) exhibiting slender, elongate bodies adapted for gleaning prey from vegetation rather than aerial pursuit. Larvae are generally terrestrial or in soil/litter predators, poorly known compared to the conspicuous adults.