Many predators kill honey bees but most of the incidental attackers have been upstaged by Varroa mites and CCD. For example, the second edition of Honey Bee Pests, Predators and Diseases edited by Morse and Nowogrodzki, devoted ten pages to various fly predators, but most recent texts on bee health ignore flies completely. Still, beekeepers are often amazed and mortified to see ordinary garden creatures snatching their precious honey bees.
Robber flies are a case in point. Robber flies (Asilidae family) are true flies that prey on other arthropods for food. Many of these robber flies will gleefully attack honey bees. Although they do not seek bees exclusively, they are often seen hanging about established apiaries where happy meals are plentiful and easier to capture than some of the quicker native insects. Some robber flies even mimic bees, making it easier for them to blend in with their prey and perhaps fooling their own enemies into thinking they pack a sting.
Like many insects, robber flies have a sci-fi way of dining: they pierce their victim’s body with a sharp proboscis and then inject paralyzing saliva into it. The saliva contains enzymes which digest the prey from the inside out. When the prey’s innards begin to liquify into a thick soup, the robber fly uses its proboscis to suck it down like a Slurpee.
Although you may not be familiar with robber flies, plenty of them are lurking in the understory. Worldwide, about 7100 species are described, with as many as 850 of those species occurring in North America alone. Robber flies have several features which—taken together—help to identify them. They have spiny legs to grasp the prey and bristly faces to protect them from prey that might bite back. They also have very short antennae and three ocelli which are located in a well-defined recess between the large compound eyes.
Considering all the bad players in a honey bee’s world, robber flies are a mere annoyance and not something to worry about. Still, if you want to write a creepy thriller, give these flies a second look.