One of the more interesting insects I have found early in the spring this year is a picture-winged fly, Ceroxys latiusculus. Picture-winged flies belong to the family Ulidiidae, and they are among the more common, ornate, and entertaining of all Diptera, thanks to their lovely wing patterns and cute courtship behaviors.
The Ulidiidae once went by the family name Otitidae, and this is where you will find them in older references. There are roughly 40 genera and 133 species known from North America north of Mexico. They are relatively average in size for flies, from 3-12 millimeters, depending on the species of course. Most have some kind of pattern of spots, bars, or lines on the wings, and at least a few have metallic bodies.
Many picture-winged flies can be reliably found on certain plants, dung, logs, rails of unfinished wooden fences, or the trunks of trees. These locations serve as food sources, basking sites, or display sites for courtship. Below is a video of behavior typical of picture-winged flies, though flies in other families also exhibit the wing-flicking thing.
Ceroxys latiusculus is common throughout western North America, especially in spring and fall. In the larval stage it develops in the seed heads of plants in the genus Senicio, known as groundsels or ragworts. The adult flies apparently invade homes and other buildings in the fall, seeking winter shelter.
Back in the eastern U.S., Delphinia picta, 7-8 millimeters, is perhaps the most common picture-winged fly. It breeds in decaying organic matter such as compost. Consequently, it is a common fixture in gardens, as well as forest edges. Look for it on foliage or the ground.
Idana marginata is our largest species, about 10-12 millimeters, and it is not uncommon in the northeast quarter of the U.S. Look for it at fresh bird droppings (yum!), or fermenting sap oozing from wounds in trees. At its size, it can easily be mistaken for a fruit fly (family Tephritidae), or some other dipteran. The larvae develop in compost.
One of the more bizarre picture-winged flies is Stictomyia longicornis, which is found almost exclusively on prickly-pear cacti in the southwest U.S., and possibly elsewhere cacti occur. Indeed, it has been reared from rotting cactus pads. The adult flies are only 4 millimeters long, but look more like true bugs or beetles than flies. The wings are short and plastered to the back of the fly. They rarely take wing, either, preferring to dodge between bundles of cactus spines.
Physiphora alceae is rather atypical in that it lacks bold markings on the wings. This species, about 5 millimeters long, is not native, but its exact point of origin is not easily defined. It is now considered "cosmopolitan," and likely to turn up anywhere in the U.S. Look for the adults on flowers. The larvae feed in decaying plant matter or animal dung.
The two species of Pseudotephretina closely resemble Ceroxys in size and appearance, but the bars on the wings are more "tiger-striped" and complete than in Ceroxys. These flies are closely associated with poplar and willow trees, but look on the trunks of cottonwoods as well.
One of the more common and attractive ulidiids to be found in southern Arizona is Diacrita costalis. It also ranges into southern California, New Mexico, and Texas. I typically found it in shaded situations during the day, such as under rock overhangs, or covered patios. They are also attracted to bird feces.
Perhaps the most adorable species are in the genus Callopistromyia. They are only 3.5-5.5 millimeters (usually on the lower end of that spectrum), but absolutely captivating in their behavior. Males can be seen on fence rails or logs where they erect their patterned wings perpendicular to their bodies, then sidle this way and that. C. annulipes is called the "Peacock Fly" in reference to this display. Here's a brief video that illustrates the behavior. The larvae live under bark, but their diet is apparently unknown. Look for these insects throughout the northern U.S. south to northern Georgia, Louisiana, Oklahoma, northern Utah, and Washington state. C. strigula occurs in Canada and the northeast U.S.
I think you get the "picture," pun fully intended. This is a diverse family of flies that for a change are rarely, if ever, pests (the six Tetanops spp. live as larvae in the roots of living plants), and that have unique behaviors and lifestyles. Enjoy hunting for them.
Sources: Marshall, Stephen A. 2006. Insects: Their Natural History and Diversity. Richmond Hill, Ontario: Firefly Books Ltd. 732 pp.
McAlpine, J.F. (ed.). 1987. Manual of Nearctic Diptera Vol. 2. Ottawa: Agriculture Canada. pp. 675-1332..