Picture-winged Flies

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My first (and not so good) photo of Idana marginata. (Kennebunk, ME)

Walking around my yard one morning a few years ago, I looked up into a maple tree to see an unbelievably beautiful insect. Golden yellow and tan, with a striking pattern of black stripes and splotches, the critter looked down at me, rowing its wings back and forth with a feeling of knowing exactly what it was doing. It was unmistakably a fly, but it was huge by Maine fly standards – about 10 mm long. It was also perched high up on the tree trunk, too high to be reached by hand or net. Luckily I had my camera with me. Unluckily, it was only my little point and shoot. I took aim and fired off three shots before the fly, well, flew. Only one photo was in focus, and since the critter was so far away, it was not a very good photo at all. Something as distinctive as this had to be identifiable, though. “Well”, I thought, “I’ll post it on BugGuide and see if anyone can point me in the right direction”. Two hours later I had my answer, courtesy of veteran BG editor v belov. It was Idana marginata, eastern North America’s largest picture-winged fly. This family, Ulidiidae, contains about 130 species in North America, many of which are very brightly colored and patterned, hence the common name. Most develop in decaying organic matter, or in roots. One of North America’s most commonly photographed flies (judging from BugGuide records), Delphinia picta, belongs to this family. It is widespread across eastern North America, and can seemingly be found in just about any habitat. Strangely, I have only run across this species twice, and both times were before I really learned to take good insect photos. This is a recurring theme for me – I seem to be good at finding scarce species, but supposedly common and abundant ones seem to slip by me. I guess it shows that our definitions of “common” and “rare” really depend on the luck of being at the right place at the right time.

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My best shot of Delphinia picta. (Eastchester, NY) Need to find another one of these!

Another interesting genus of Ulidiids is Chaetopsis. This group includes about 7 species in North America, several of which are confined to various types of marshes. One species that I found last year, C. aenea, is a specialist feeder on Spartina grass. This grass is the major component of East Coast salt marshes. Guess where I found my specimens?

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Chaetopsis aenea, found on Spartina grass. (Scarborough Marsh Audubon Center, ME)

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Another species of Chaetopsis, probably C. massyla, which is found in freshwater marshes in the eastern U.S. (Sanbornville, NH)

I found my second individual of Idana marginata about a week ago, again in my yard. I was looking out onto my back deck from inside, and spotted it sitting on a deck chair. In a minute I was outside with a vial, and quickly snapped up the animal, still warming itself in the morning sun. This time I was finally able to get some good photos of it. Amazing to think that such a beautiful animal can arise from a backyard compost pile. Actually there are a ton of interesting life forms to be found in compost, but I’ll leave that for another post.

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Idana marginata (Kennebunk, ME)

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Face-to-face with the subject of this post!

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One thought on “Picture-winged Flies

  1. Pingback: Getting their Feet stuck in the Milkweed | The Incorrigible Entomologist

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