The amazing robber fly

September 24, 2013 • 12:01 am

by Matthew Cobb

While I was asleep, my Tw**ps were chatting about robber flies. So I woke up to these great pictures. Robber flies – technically the family Asilidae – are strong and agile predators that as adults feed on other insects, sometimes much larger than themselves, catching them in the air. The result of such a chase is shown in this fantastic  photo by Sarah J. Semmler (@SarahSyrphid), showing a robber fly that had just grabbed a meadowhawk dragonfly:


What a fantastic photo! Sarah also tw**ted this photo of a robber fly by Seth Patterson from Bugguide, pointing out the well-developed ‘claws’ on the end of the tarsi, and the spines all over the legs which would make it easier to grab prey in the air.

Robber Fly - Efferia albibarbis - male

They will eat anything, including stuff much smaller than themselves, as seen in this photo by Muhammad Mahdi Karim of a Pegesimallus fly nomming what looks like a small fly:

File:Pegesimallus sp robberfly.jpg

And look at this, the massive ‘Florida bee-killer’,  Mallophora bomboides, photographed by Nancy West, University of Florida. That’s a honey bee it’s eating!

The "Florida bee killer," Mallophora bomboides (Wiedemann), with honey bee prey

And people think that mammals are beautiful predators!

According to Wikipedia (sorry) there are over 7,000 species of Asilidae. You can find tons of stunning photos on the internet.

Although the life-style of adult robber flies is well known, the ecology of the larvae – which interest me – is much less well understood. Larvae of some species appear to be classic detritus-feeding maggots, while others are reported to eat insects but mainly eggs and other larvae (i.e. they bumble across them, perhaps guided by smell and taste, rather than being cunning predators).

22 thoughts on “The amazing robber fly

  1. Amazing indeed!

    And fabulous pictures. I love the way the robber fly in the third photo is just nonchalantly hanging by one leg.

          1. I’m not sure! I know a lot of crane flies (Tipulomorpha) tend to hang from various substrates, but I’d guess this is more of a function of their delicate legs rather than a strategy.

  2. Found this amazing quote on the BugGuide site: “Cockroach wasps temporarily paralyze the adult cockroaches using venom. While paralyzed, the wasp makes a second sting, this time using venom inserted into a precise location in [the] cockroach’s brain. The antennae of the cockroaches are then clipped, and when the paralysis wears off, the wasp leads the cockroach to its lair. The cockroach makes no attempt to flee as an egg is laid upon it. When the eggs hatch, and the helpless cockroach is devoured by the young maggot-like wasps.”

    You can hardly make this stuff up…

  3. The Pegesimallus fly also looks (from the shape and colour of the abdomen) as if it might be mimicking an Ichneumonid wasp. A male wasp anyway, it lacks the jutting-out ovipositor of a female wasp. Intriguing!

  4. The robber fly certainly has a fierce look with it’s spikely legs & ocular fringe. The size of it’s compact eyes are impressive as well. I wonder if they have hunting advantages over the many eyes of a spider.

  5. Robber flies are very interesting. Can I say cool? That’s what I really mean.

    I have one or two good pictures myself of an unknown (to me that is) robber fly my daughter and I came across. Not quite the quality of these pics though. One stand out feature was bright yellow feet on black legs. Similar to the third pic above, but otherwise different.

  6. Thanks for posting on robber flies. I took some photos of one similar to Seth Patterson’s last June. I knew I had seen the type of fly before but couldn’t remember the name and my searching for a name wasn’t fruitful. Mine was apparently a male slurping on a house fly.

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