What kind of cave? This is very interesting, cause I am working on this genus (there are 2 species in AZ, one of them is undescribed and there is a third undescribed species in Utah). A big unknown are the larvae of this very odd (and maybe most primitive) genus. All Therevidae larvae are predators in the soil, but nobody ever found the larvae - and I am very interested in them. My theory is that the larvae are living in tree holes or caves, cause the adults are often find inside buildings. So they have the tendency to fly into dark openings. the same behavior I noticed in some syrphids which lay their eggs in hollow trees - they also fly inside buildings and are found on the windows. So I am very excited to hear that you found the adults in a cave! And I thought if they are really inside trees, the beetles guys rear out beetle larvae from inside trees, so I thought they would have found Henicomyia in the past... So maybe they really live in caves. Which would also be a good habitat for a relict species... So all is needed is somebody with mesh (pool leaf remover etc) and sieve through the soil and find some of the white worm like larvae! Great pics Keith by the way!
Cheers
Martin

The cave was a hole in a rock wall maybe 10 yards deep at most. Leaf litter and soil from the outside covered the ground. May have been deeper but didn't really venture into it as I didn't have my head lamp. In the cave were also Bombyliids, Tabanids, and various other insects so still a chance it was just cooling off (it was near 100 that day but much much cooler in cave). The exact location of this "cave" is as you go into the Chiricahua Mountains from Portal, on your left near the bridge crossing into one of the campgrounds (Cave Creek maybe?) There was maybe 30 feet of forest vegetation and then a rock wall and the cave was here. The rocks in that whole area are riddled with nooks tiny caves and apparently some larger caves.

the biology of this species. all therevid larvae, as far as is known, are predators in soil. This genus is one of the only ones in its subfamily, the Xestomyzinae, in N. America.

could you post the shiny green Syrphids from Cochise's Stronghold and the fly I got you last year from just south of border?