Observations by owicki

Looks like this is a parasitoid on Coyote Bush Bud Gall Midge, Rhopalomyia californica.

I'm just guessing on the species because Russo says that Platygaster californica is the most common parasitoid on the galls and photos I've seen are roughly the same. But I gather that there are a handful of others, some from different families like Torymidae and Pteromalidae.

The other photos show the twig and the wasp apparently ovipositing or getting ready to do that.

Several of these flies were hanging out at a Pheidole ant nest where something strange was going on, maybe an attack by Neivamyrmex army ants. I suggested that the flies might be phorids mostly because they're little, kind of chunky, and associated with a possible phorid host. I wish I had a better photo, but I never saw one land.

BL 5 mm

Note the powerful forelegs.

PME about equidistant between ALE and PLE, which wouldn't be typical of Sassacus.

Second photo shows it in the retreat it spun in the collection vial.

Collected (with permission) and released after photography.