A Picture-winged fly from League City, Texas

Picture-Winged Fly (Delphinia picta); Mark Turvey, Humble, TX--3 Nov 2010

Mark Turvey is a regular contributor to Bugs In The News. He recently sent me several photos of an unusual ant he found near his home in Humble, Texas. Along with the ants, he noticed flying insects nearby that he thought might be associated with the ant colony. He wrote:

Jerry

I found a dirt tunnel on the foundation to a cinder block building that had some strange looking ants crawling on it. These appeared to be longer & skinnier than normal ants, When I broke the dirt tunnel it was filled with lots of smaller ants. A few of the ants were winged. I’m thinking there was a void access into a hollow cinder block & the ants may have colonized up into it. I have attached a few pictures.

Mark

The only flying insect included with Mark’s photos was a single image of the insect shown at left. My initial reaction on viewing this image was that it depicted a wasp. However, on closer inspection–aided considerably by the shadows cast by various anatomical features of the subject specimen–it was clear that it had but two wings (notice the shadow cast by the wings on the rock the fly is resting on) and must, therefore, be in the order Diptera, or true flies. Notice, too, that the shadow cast by the head shows two small, stubby antennae, precisely as would be expected in a fly.  A wasp, in the order Hymenoptera, would have four wings.

The order Diptera contains in excess of 240,000 species of mosquitoes, gnats, midges and other flies. Less than half of these have been described, and it can honestly be said that man is largely ignorant of their most superficial biological natures, particularly those that reflect on the ways they interact with us. Don’t say that too loudly, though, as many practicing biologists have–for at least a century or more–believed they knew all they needed to know about flies. That “knowledge” so informed us, in fact, that we grew to believe that the only good fly is a dead one.

In a way, one can understand why.

Many flies, including the mosquitoes (Culicidae), are efficient vectors of diseases such as malaria, dengue, West Nile virus, yellow fever, encephalitis and others, often inoculating their hosts while obtaining a blood meal. Others, such as the common house fly, spread disease mechanically by contaminating the surfaces of food materials while feeding on them. These negative effects have led us to view all flies in a negative light. This is not reflective of reality, however, as many more of our flies benefit, rather than harm, mankind. Tachinid flies, for example, look exactly like common house flies to the naked eye, but without them we’d likely be overrun with the noxious caterpillar infestations that these flies so effectively control.

The picture-winged flies appear to be beneficial flies as well, though not much is known about them.

Several picture-winged flies native to North America are commonly confused with fruit flies. Were they comparable, in terms of biology and habitat, that would not bode well for the picture-winged flies, as fruit flies deposit their eggs in living, healthy plant tissue and their larvae live and feed on the host plant. By contrast, the larvae of most species of picture-winged flies (today classified under the family Ulidiidae) are saprophagic, that is, they feed on dead, decaying tissue.

Of course, a few picture-winged flies, such as Tritoxa flexa (Wiedemann) and Tetanops myopaeformis (Röder), are known to attack living plant tissue.

The larvae of Delphinia picta (Fabricius), the subject of this article, does not. The larvae of this fly can be collected from fallen ripe plums that are grossly decayed, but they have never been found to  attack fresh, healthy fruit.

According to Allen and Foote (1967):

“In northeastern Ohio, adults . . . were found from mid-May until late summer. The premating period averaged less than two days; the preoviposition period after mating was three to seven days. Field-collected females each deposited 400 to 500 eggs in decaying herbaceous vegetation. Eggs hatched in four to seven days, and larvae given rotting vegetation completed their development in 20 to 31 days. Larvae of the first generation pupated, with adults emerging 12 to 15 days later, but increasing percentages of the larvae of the second and subsequent generations entered diapause.

“Overwintering took place as diapausing mature larvae in the soil. In early May, perhaps in response to warming soil temperatures, the larvae migrate toward the ground surface and form puparia. The rearing records indicate that D. picta is a multivoltine species, with a facultative larval diapause which probably is induced by decreasing day lengths. Adults reared from puparia usually lived less than 40 days in the laboratory, although one female remained alive for 69 days. Males generally died first. Mating occurred within two days after adults emerged in the breeding jars. Mating occurred repeatedly during the life of the female, with each mating lasting approximately an hour.”

It is possible that this fly was associated with the ants Mark saw, particularly if those ants cultivate fungus gardens that grow on decaying vegetation.

jc

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