Yes this is a botfly for sure. These guys are of huge interest to me. Up here in the Northeast this species seems to primarily use chipmunks as a host. South of VA these guys use squirrels as a host. They may turn out to be two species or closely related sub species. If you collected this one, I would love to be able to use it for dna work to see if these are two or one species. I have another bot I got from Tucker on BugGuide from the south and a lot of northern specimens, but I could use more from the south to try to figure out the story. A really fun find. Our only yellow rodent bot in the East.
Thanks for posting the nice pics.
Jeff Boettner
boettner@psis.umass.edu

First I thought a Bumble bee, but then I noticed its attitude was not the attitude of a Bumble bee: it was very excited, flying fast from one stick to the other, close to the earth, and rubbing its "tail" (anus?) against them, as you can see in one of the pictures.

There's plenty of chipmunks and squirrels in my backyard. Sometimes we've seen the squirrels, for a number of weeks, with what looked like a tumors, but now I think it could have been these flies.

Martima,
Yes the tumor like lumps you see on the squirrels is likely due to this fly. The behavior you describe fits for egg laying behavior. You may see squirrels with lumps in about a month from now. Takes a while to get big enough to notice. What is weird about these guys is that they are mostly using squirrels down by you, even though you have lots of chipmunks. Up here in the north these flies use chipmunks and rarely hit the squirrels. It would be interesting to know if these are actually two cryptic (look alike) species or else why such differences in the north and south.
Jeff

I did not collect it, but will keep an eye on it, and the squirrels and the chipmunks.

Thanks for keeping an eye out. Its a really fun find. The bots are not rare, a large percent of squirrels get them, but adults are rarely seen in the field. So you are one of the lucky ones to see it. I have not been down in the South at the right time to hunt for these, but have seen them a few times up here.
Jeff