I think I have photos of this or other individuals, perhaps from different angles. Would any particular views or photos of other individuals be helpful?

The best way to identify this fly is probably by looking under the scutellum for a row of erect bristles. This will immediately confirm the genus Stonemyia, since this trait separates this genus from what it appears to be all genera of horse flies in the US. If not, the best bet may be to find more of these and photograph them...maybe this is an aberrant individual.

My thought process;

- Vein R5 does not slope down to vein M1; eliminates Esenbeckia
- Vein R4 is without an appendix; very rare occurrence in Stonemyia californica and genus Pegasomyia
- Orange femora and western distribution; Stonemyia californica is the only extant species in the genus with this combination, not sure about S. velutina but that's been declared extinct

I have posted photos of two other individuals that were taken nearby on the same day:



I couldn't get very close to these two flies, so they were very small small in the photos, and I've enlarged them for posting. It looks to me like they do have an appendix on vein R4. What do you think?

I couldn't tell if there were bristles under the scutellum in any of the photos.

I'd also want to say how much I appreciate your posting your reasoning. I am relatively new to the world of insects and learning what to look for is really, really helpful! Thanks!!!

Yes, I see the appendix! So these are either Stonemyia californica or Pegasomyia. Since they look much different from the S. californica, the bristles under the scutellum may have become necessary for identification...sorry, but there's potential it could be the first definite live photo of a Pegasomyia, and a confirmed Stonemyia californica too! Because, honestly, I'm not sure about the current photos of those two we have.

I wish more of BugGuide's experts were active here. You don't know how much I appreciate users when they go through the effort to help identification! It's a learning experience for me as well.

I'm afraid not. The wing venation is clear, but I know of no species of Esenbeckia with this wing venation. It also doesn't appear to resemble or fit any of the Stonemyia I know.

Tony-2 (Anthony W. Thomas) identified Individual #3 as Pegasomyia. See comment here.

I've also posted more photos taken by Vicki Salazar, who was with me, here.

I think it is likely. I wish I had specimens of Pegasomyia and Stonemyia californica. It does fit the description of female Pegasomyia, which may be impossible to identify to species (perhaps except for males).