Digging Wasps

Parasitic Flies

This tiny fly species was abundant at the college site (see page 1).

I shot a short video of the site to show the amount of activity. Two specks enter the frame from the left, with one closing on the other.

Here’s a 1 frame/second clip from the original movie (taken at 15 frames per second), with the flies denoted by arrows.

Both flies fell to the ground, rolling around for several seconds. I switched to photo mode and got some stills of the pair (lower left), then caught one of the pair and photographed it at home with a microscope (lower right).

Using this key to Conopid flies, I tentatively identified this fly as a member of the genus Thecophora (fly on thumb for scale). Conopid flies parasitize hymenopterans, so this species is probably congregating on the site to parasitize the various hymenopterans there. Conopid flies waylay their hosts in flight, laying an egg that matures into an internal parasite.

This pair appeared to be mating, and I observed similar behavior on subsequent visits to the site.