honey bee threats predators

Flies with a wicked thirst

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.


Common brown robber fly catches a hover fly. Photo by Fir0002/Flagstaffotos.

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  • Rusty, you sure have a great way with conjuring up mental images – Slurpee indeed! Yup – been there, done that. Watching my hive one day this “insect” flying nearby. I gave it a casual glance and noticed its sharp buzzing sound as it landed. Just about the time I said “Hmmm,” it grabbed one of my bees in an instant. Yes, I was astonished! I must admit I giggled at myself as I ran after the thing, arms flailing, yelling “Hey! Give me back my bee!!” I went into the house and did a quick insect id to add one more insect to my fast growing entomological vocabulary. Robber bee. Now, The Dreaded Robber Bee.

    • It’s funny. In spite of entomology courses in college, I didn’t learn about bugs until I began keeping bees. It makes it all more real.

  • Well, years before I ever had hives, I learned about robber flies from gardening, which had me working alongside dozens of peacefully foraging bees. And maybe they don’t do that much harm, in terms of hive numbers, but I will still catch and squush them when I have a chance. I think they are either intimidating the bees away from my 30 x 30” stand of blooming buckwheat, or just catching the scouts before they can go back and tell their sisters how to find it!

  • Rusty, that’s a nice photo! Great work! Robber flies are very quick and very alert. Most of the time they do not fly very far from where they are flushed but they will repeatedly fly which makes getting a photo like you have here very hard to do. I’ve noticed several sized robber flies around here. So far I’ve seen them with several victims including yellow jackets….no honey bees so far! 😉