Two Picture Winged Flies including Black Onion Fly and a Signal Fly

3 different flies with patterned wings
November 29, 2009
Here are 3 similar but different flies that were all sitting near each other. Two were perched on squash leaves in a vegetable garden. The very black one (in the last photo) was nearby on a wall near a sunflower. I took the photos on July 23rd and it was a warm sunny day. They were all smaller than the common housefly. And the black one was larger than the other two. They all look related but the wing patterns are different on each one. The 2nd pic fly is eating a bird (or teeny lizard) dropping. Could one (or more) of them be a walnut husk fly? Our neighbor has a walnut tree. Is it just a coincidence that they are hanging out together?
I aalso have photos of a green jumping spider protecting her eggs…I photograghed daily until the eggs hatched, little spiderets everywhere and mom had left. I don’t need any identification, just wondering if you’d like me to send some pics of the process.Thank you……
Fredericksburg, VA

Black Onion Fly
Black Onion Fly

Hi swarner,
We have been very busy recently, and today we are randomly selecting older letters to look for good postings.  Your photos are awesome.  We believe all three of your flies may be Picture Winged Flies in the family Ulidiidae, and we have conclusively identified the Black Onion Fly, Tritoxa flexa, on BugGuide.  The species if found over much of North America, and it is associated with cultivated garlic.

Picture Winged Fly

A second Picture Winged Fly is Delphinia picta, also found on BugGuide, and it breeds in compost piles.  The two white triangles on the leading edge of the wings is a distinguishing feature.

Signal Fly

Continued searching revealed your final fly to be a Signal Fly in the genus Rivellia.  According to BugGuide, they are found on foliage feeding on feces, exactly as your photo depicts.

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