I saw this pair of Small-headed flies, Eulonchus tristis, on a salmonberry leaf (Rubus spectabilis) at the edge of the woods near our house* (06 27 2007). They were so busy mating, apparently, that I was able to take a number of photos from various angles.

• Periodically, the male vibrated his wings (photo 3).

• Photo 2, especially, shows how small the head is in comparison to the thorax and abdomen.

• The female was about 3 cm in length (photo 5).

• Both sexes have relative simple, slender conical antennae, and a crease in the side of the very bristly eye, photo 6, a feature less obvious in the male.

   Female head top view | Male head top view

While I didn’t get a good transmitted-light image of the wing veins, a zoomed close up of the wings does show the 3D nature of the wings (similar to all fly wings).

Identification features for this species include that the margin of the squama is not pigmented
   (sq=squama, a flap at the base of fly wings; hal=haltere).

Small-headed flies, family Acroceridae, are relatively rare flies that may feed on flowers as adults, or may not feed at all as adults. They lay eggs on leaves, which hatch into tiny, flat larvae that then burrow into a passing spider, later emerging to pupate on the web.

* About 2,000 feet elevation, five miles south of Port Angeles, WA.

• Thanks to Eric Eaton and Dennis Haines at bugguide.net for identification.