Robber Fly

 

common name: robber flies
scientific name: Asilidae (Insecta: Diptera: Asilidae)

The robber flies are an abundant and diverse family (Asilidae) known for their predatory behavior. Asilidae diversity can be attributed to their broad distribution, as most species tend to occupy a selective niche. As their common name implies, robber flies have voracious appetites and feed on a vast array of other arthropods, which may help maintain a healthy balance between insect populations in various habitats (Joern and Rudd 1982, Shurovnekov 1962). Asilidae adults attack wasps, bees, dragonflies, grasshoppers, other flies, and some spiders. Robber flies are particularly abundant in arid and sunny habitats, which are optimal conditions for observing their many morphs and behaviors.

Robber flies are opportunistic predators, their diets often reflecting prey availability in a particular habitat. Shelly (1986) reported that of the nine Neotropical Asilidae species he studied, diet constituents were more than 85% composed of insects from the orders Diptera, Coleoptera, Hymenoptera, Hemiptera, and Lepidoptera. Furthermore, larger species tended to consume a greater diversity of prey taxa. Robber flies generally establish a perching zone in which to locate potential prey. Perching height varies by species, but generally occurs in open, sunny locations. Asilidae seize their prey in flight and inject their victims with saliva containing neurotoxic and proteolytic enzymes . This injection, inflicted by their modified mouthparts (hypotharynx), rapidly immobilizes prey and allows digestion of bodily contents. The robber fly soon has access to a liquid meal, which is generally consumed upon returning to a perched position.

Robber flies exhibit minimal courtship behavior. Instead, the male pounces on the female much like an act of prey acquisition. Copulation is accomplished in a tail-to-tail fashion with the male and female genitalia interlocked. Flight is not completely inhibited during mating.