What's That Bug? does not endorse extermination

Subject:  What type of fly is this?
Geographic location of the bug:  Brantford, Ontario
Date: 07/26/2019
Time: 11:26 AM EDT
Your letter to the bugman:  Hello Bugman,
I am hoping that you can help me identify this fly. I was leaning toward a type of syrphid fly but could not find a match online. Any help would be greatly appreciated.
Thanks!
How you want your letter signed:  Dan

Signal Fly (left) and Red Milkweed Beetle

Dear Dan,
The image of the Fly with the Red Milkweed Beetle is an easier image for identifying purposes as it clearly shows the wing pattern on this Signal Fly in the genus
Rivellia which we determined thanks to images posted to BugGuide where it states the habitat is “on foliage, feces.”  We tried to determine if there is a relationship between Signal Flies and milkweed, and we located this BugGuide image and this BugGuide image and on The Pathless Wood we found an image and this information:  ” I did come across this interesting fly in my search, however, and later determined it is some sort of Signal Fly, a member of the Genus Rivellia. These flies are often difficult to identify from photographs alone; they are quite small, and identification depends on the presence or absence of tiny hairs called setae on the dorsal thorax, as well as the colour pattern of the wings and legs. They get their name from their patterned wings, which they tend to wave around as if signalling other individuals. I didn’t see this behaviour as this individual rested on an unopened milkweed blossom, so I was immediately taken with the unique pattern of its otherwise clear wings.”   So, for some reason, Signal Flies are attracted to milkweed, but we are not certain why.  Are there soybean fields nearby?  Your individual reminds us quite a bit of the Soybean Nodule Fly, Rivellia quadrifasciata, which is also pictured on BugGuide.

Mating Signal Flies

Hi Daniel,
Thank you for this information. There was a soybean field right next to this patch of milkweed so I think it may be safe to say Rivellia quadrifasciata is a match. I’ve seen other flies exhibit this behaviour of waving their wings around. Now I know where to start when trying to identify them.
Thanks again!
Dan

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What's That Bug? does not endorse extermination
Location: Brantford, Ontario, Canada

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