Robber Fly, NOT Syrphid Fly

Subject: Tiny, graceful, and apparently not a fairyfly
Location: southern California
October 25, 2013 9:19 pm
Hi again! I’ve written in a few times, and am very grateful for the identifications. I found this little flying beauty on one of my bug walks in southern California today (October 25). It is in a garden; there is a stream nearby, but not immediately proximate to this plant. The insect is about the size of a mosquito. With its long, delicate abdomen, it looked like a fairy to me when it was in flight, but as far as I can tell the term ”fairyfly” is applied to a totally different kind of insect. After spending some time unsure of where to even begin in identifying this lovely creature, I’m conceding defeat. Can you help me?
Signature: Amanda

Possibly Syrphid Fly
Robber Fly

Dear Amanda,
We really wish your photo revealed some individual features of this unusual insect.  The head and eyes look like those of a Fly in the order Diptera, and the body most closely resembles that of a wasp in the order Hymenoptera.  The fly family Syrphidae contains many individuals that mimic stinging Hymenopterans, so that is our best guess.  We were unable to find any matching images on BugGuide, but we did locate two that are somewhat similar, including
Baccha elongata and Pseudodoros clavatus.  Though they look somewhat similar, we are quite certain neither of those is your species.  The hind legs on your individual are very distinctive, which should aid in the correct identification.  We are going to contact Eric Eaton for assistance.

Possibly Syrphid Fly
Robber Fly

Update:  Bee Fly is Another Possibility
We are now entertaining the possibility that this might be a Bee Fly in the family Bombyliidae as there is a similarity to the genus
Systropus that is pictured on BugGuide.

Correction Courtesy of Eric Eaton
Hi, Daniel:
This is actually a robber fly in the subfamily Leptogastrinae.  Most of the genera have this skinny appearance.

Thanks very much to you and Eric! I had actually briefly entertained the idea of a robber fly because of the way it was hanging, but I just thought it was much too small so I didn’t look closer at that idea. That’s great to know.


1 thought on “Robber Fly, NOT Syrphid Fly”

  1. I contacted entomologist friend Jim Hogue, who offers this comment which takes the ID to genus: “This fly is an asilid in the genus Leptogaster. Notice the position of their legs (kind of like a damselfly). These apparently (from talking with a friend a few years ago that works on this genus) carefully fly around spider webs and take food items out of the webs to eat. I don’t think they take spiders though. They are kind of like those giant neotropical damselflies that steal from spider webs and do take spiders. I couldn’t say what species this is.”


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