j.g.medot's picture

Parasitic wasp ?

Observed: 15th July 1999 By: j.g.medot

That the observation suggests a parasitic wasp is a guess on my part, therefore I can only explain what I observed (taken from notes I made at the time).
It was a very warm day and flying ants were emerging from a nest behind some concrete steps. They were black ants, but which species I don't know. Whilst watching the ants, I noticed a very tiny fly hovering above the scurrying workers. The fly was c.a. 1mm-2mm long with a very narrow body, which appeared black. The wings were too small, or fast, to be seen. Occasionally the fly followed a particular ant, hovering above and slightly behind it, as it ran. Suddenly the fly dropped onto the ant's forward abdomen and flew off immediately. The entire cycle of following, diving and flying off appeared to happen in a fraction of a second. As the fly landed, on the ant, the ant momentarily hesitated and arched it's back. This happened several times and one particular ant was moving so quickly that as it jerked, with the arrival of the fly, it's momentum caused it to tumble and roll completely over.
During the time of the observation the fly rested a few times. Even when it was resting I was still unable to see the tiny wings. Unfortunately the fly suddenly disappeared and I was unable to catch it for identification purposes. Was this the action of a parasitic wasp?

Species interactions

No interactions present.


Martin Harvey's picture


That's an interesting account, and yes it does sound as if it could be a parasitoid of some sort. There are some parasitic wasps that lay their eggs onto adult ants, but there are rather more species of flies in family Phoridae that also target adult ants, so that may be what you saw.

There's some information in this presentation from the University of Utah (pdf download):

Entomologist and biological recorder