October 19, 2009
On Saturday (October 17th) our local Audubon club came across a rabbitbrush in full bloom. There were a lot of bugs visiting the bush, including what we first assumed were lots of bumble bees. As we got closer it became obvious they weren’t bumblebees, and we were undecided if they were actually bees or flies.
Saint George, Utah
Your fake bumblebee is actually a Tachinid Fly. Tachinid Flies are parasitic on other insects, and according to BugGuide, caterpillars are a common host. We are not certain of the exact species as there are many similar looking possibilities, including Adejeania vexatrix and Hystricia abrupta, though our top choice is the Spiny Tachina Fly, Paradejeania rutilioides. According to BugGuide, Spiny Tachina Fly: “Adults take nectar, especially from late blooming Asteraceae.
Larval host: the arctiid moth Hemihyalea edwardsii (at least in part of its range …)” The other insect in the one photo appears to be a Sand Wasp, probably in the subtribe Bembicina, though exact species identification may be impossible.
Thank you! I think our Audubon group will be very interested to learn what they were- even though we are mostly bird nerds 🙂