What do you call a fly that eats grasshoppers, bees, and even dragonflies? Assassin fly is one common name, but they’re most often known as robber flies. 

Flies in the Asilidae family have several distinguishing characteristics. Their eyes are bulbous, and separated by a large indent. They have a beard, called a mystax, made of bristly hair that protects them from struggling or stinging prey. There’s also a prominent, pointy proboscis. This instrument has multiple uses. It injects neurotoxins and digestive enzymes to subdue and dissolve its prey, after which, the proboscis serves as a straw to consume the now liquified meal. Nature’s own NutriBullet, if you will. 

The flies I saw at Mount Pisgah lately are in the Eudioctria genus, and the red-legged species with a lunchtime weevil is Eudioctria nitida. Robber Flies have specialized sections on their compound eyes enabling them to focus on moving prey. Asilidae flies fly so fast it’s hard to track in real time, but they actually slow down and turn at the last moment to snatch the prey in mid-air, using the stiff hairs on their legs as grippers. There’s a great video online of this maneuver. Look it up! It’s called “The Robber Fly: Top Gun of the fly world.”

There are several other genera of robber flies in our area. Some of them are credible mimics of bumble bees. I hope to highlight them in the future. 

Stay curious!

See more of Karen’s work here.


Account of a robber fly attacking a hummingbird: http://www.hiltonpond.org/ThisWeek070901.html. Accessed 7/1/22. Look about halfway through the article, after the picture of the two people. 

General information on the Asilidae family: https://www.colorado.edu/asmagazine/2020/02/28/robber-flies-are-fierce-predators-and-resourceful-lovers. Accessed 7/1/22.