Probably native to North America, but found in many other countries as well.
This is one of several small flies in the genus Fannia, whose males tend to hover aimlessly and for long periods in shaded locations, such as patios, breezeways, open garages, or shaded garden areas. Larvae breed in any of the typical decaying organic matter situations that other filth flies do, such as animal feces, decomposing piles of lawn clippings, or filthy garbage containers. Adult flies feed on sugary materials, and honeydew accumulations on plants may draw them. The period from egg to adult averages about 3 weeks, and adult flies live from 2 to 3 weeks. The larvae tend to move to the surface of their food material, or wander away from it, just prior to pupation.
The adult flies resemble House Flies, but are about half the size and with much thinner abdomens. The males have dark yellow patches on the sides of the abdomen, while the females are gray. The wing vein patterns of the flies are distinctive, and on the flies of the genus Fannia the middle vein runs almost straight out to the tip, while on the House Fly that same vein has a 90 degree upward bend. The eggs and larvae of the Little House Fly are very different looking. The eggs are flattened and veiny, with float-like flanges on each side that enable the eggs to float in very wet media. The larvae are covered with spiny projections along their top and sides, and turn from white to brown as they mature.
Characteristicts Important to Control:
Elimination of breeding sites for the larvae is extremely important, and in an urban setting this may be pet feces in yards, filthy garbage cans, or piled, decomposing lawn clippings. In rural areas the accumulation of livestock or poultry feces will produce vast numbers of flies. Proper exclusion from structures involves keeping doors and windows screened or closed, and the use of UV light traps will capture many adults indoors. Outdoors the use of fly bait strips or granules will be effective in killing adult flies. In locations where the adult males choose to hover continuously they can be discouraged by increasing the air movement through the area.