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Robber flies grab bees in flight

Two of these photos arrived this week with the same question, “What is eating my bees?” The top photo, taken by beekeeper Wayne Gillispie, came from northeastern Kentucky. The second, by beekeeper Roger Taylor, came from Gallatin, Tennessee. Each predator has a honey bee in its jaws.

These creepy-looking bugs are in the family Asilidae and are commonly known as robber flies or assassin flies. Based on the photos, it might seem like they have a predilection for honey bees but, actually, just about any insect will do for a midday snack.

Feasting on insects

The family is huge, comprising about 7000 species, and they all eat insects. Many of them enjoy meals that are large and feisty, so they will go after dragonflies, wasps, bees, grasshoppers, butterflies, moths, and beetles. Most have spiny legs that aid in capturing prey in the air and holding it still.

Once an insect is captured, the fly stabs it with its proboscis and injects paralyzing enzymes. In time, the enzymes digest the insides of the prey and the robber fly sucks it out, like coconut milk through a straw…or a protein-fortified smoothie.

Incidental predators on bees

Robber flies occur nearly everywhere, but more species are found in places that are open, warm, and sunny. They are only incidental predators on honey bees and nothing for a beekeeper to worry about. Just keep taking those cool photos.

Rusty
HoneyBeeSuite

Wayne-Gillispie-robber-fly
A robber fly in northeastern Kentucky. Photo © Wayne Gillispie.
Roger-Taylor-robber-fly
A robber fly in Gallatin, Tennessee. Photo © Roger Taylor.
Mike-Smith-Robber-fly-650-px
Face to face with a robber fly. © Mike Smith.

Comments

Merilyn Thomas
Reply

In Australia we have birds called Rainbow Bee Eaters, and according to wikipedia they migrate from southern Australia to northern Australia in winter. These birds are really beautiful with feathers like the colours of the rainbow. We have long seen them on our land, but since we have had the hive, I think their population has increased. Last year I noticed several bees on our car and around the yard with no abdomen, some still alive with moving leg. I wonder if they were the prey of the rainbow bee eaters who eat the abdomen and ditch the rest of the body. The wikipedia page describes how the bee-eaters deal with eating the bees. http://en.wikipedia.org/wiki/Rainbow_bee-eater

Rusty
Reply

Thanks, Merilyn. That is interesting, and they are very pretty birds. It is sad, though, when predators don’t kill their prey outright. I hate to see things suffer.

Merilyn Thomas
Reply

After reading your posting, I have checked on wikipedia to see if these are present in northern Australia and yes, we have heaps, including many undescribed species. I will keep a closer eye out now I know about them. I probably thought they were some sort of large bee or wasp as they look less like the usual fly. http://en.wikipedia.org/wiki/Asilidae

Linda Rivers
Reply

I have seen these insects around the barn, and our livestock guardian dogs run away from them. I thought they were horse flies, but it’s interesting to learn they are robber flies. Thanks for the information, Rusty.

Rusty
Reply

Linda,

I’ve heard their bites are nasty, so it is not surprising the dogs run from them.

Nancy
Reply

“Incidental predators” on honey bees? Rusty, please.

I have found them perched on a sunflower, with a pile of bee parts on the leaf below them, clearly waiting for more. Given the recent study showing that 30% of a colony’s foragers account for most of the gathering, over a period of weeks there could be a cumulative effect. Or, if one picked off a scout, a patch of important forage could go unharvested.

And, they are on the increase, owing probably to climate change. Species that used to make 1 or 2 broods a Summer (squash bugs, Colorado potato beetles, stinkbugs) are now making 3 or 4, with exponential effect. Formerly greenhouse pests, like whitefly and mealy bug, are now being found out in the fields.

Where I used to see one robber fly a season, I now see 3 or 4 a week. It may be that I now have beehives, of course, but that’s hardly incidental, is it?

Anyway they are about as agile as a horsefly, so I grab and smush them whenever possible.

Nan
Shady Grove Farm
Corinth, Kentucky

Rusty
Reply

Nan,

I see your point, but I still think they are incidental, especially compared to something like a mite infestation that can affect every bee in the colony. Also, the same article (if it is the same one) said that if you remove the 30% doing all the work, they will shortly be replaced.

My point in this series of articles it that there are hundreds of honey bee predators, including insects, spiders, birds, mammals, frogs, snakes, and humans with spray cans, but it really only the mites and diseases that consistently wipe out hundreds of colonies.

Glen Buschmann
Reply

With 1500 eggs laid by queen in a day, I have to side with Rusty over the term incidental. Unless these predators could reach and kill the hive’s queen on a continuing basis, (highly unlikely), a few bees a week (out of 10,000 eggs laid) is nothing. They might pose more of a threat to a small insecure bee colony like a newly emerged bumblebee queen trying to establish a new colony — but they are opportunistic hunters, and I’ve seen them carrying wasps, butterflies, and I believe a grasshopper too.

Anna
Reply

I have wheel bugs stationed on my hive tops and on hive corners. Since they are (thankfully) everywhere else in my garden too, I just leave them be and let them catch a few bees in exchange for eating all my bad bugs.

I never get tired of looking at them as they are so primitive looking.

Rusty
Reply

Anna,

Okay, I just learned something . . . never heard of wheel bugs before.

Bill R
Reply

Nice photos! Haven’t seen any around this year.

Doug Victory
Reply

These robber flies have eaten 2 of my queens while working my bees. As I was inspecting my bees and found the queen, as she climbed to top of frame, all I saw was a blur. Then I watched this robber fly take my queen and was gone but I did see what it was just for a second, as I have seen them around my apiary once in a while. Now I will not work my bees if I see one around. The 2nd queen was taken while my brother was working our bees and it did the same thing. That apiary was 80 miles away almost the same day as we talked on the phone that evening, and like me beyond surprised, so my advise is to be cautious when working your bees, this robber would land on my hives a little ways from me, didn’t think much about it, then it’s too late. I also think when some queen’s don’t make it back from their mating flight, here’s why.

Rusty
Reply

Doug,

I wonder why they selected the queens. Weird.

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