In houses the flies are found around overripe fruits and vegetables, especially when they begin to ferment. They may also be attracted to bread or other baked goods containing yeast, and to beverages including fruit juices, soda pop, beer, and to vinegar. On occasion you may see one on a moist washcloth or sponge near the sink getting a drink of water. They can be annoying flying around, but they do not bite.

The flies are relatively small, 3-4 mm in length, and brownish to yellowish in color. Many species have red eyes. They generally are found around decaying vegetables and fruits. The larvae are seldom seen, but occur inside the decaying food and are whitish in color and wormlike in appearance.

Several species of this group have been used in studies of genetics and heredity by scientists because of the ease in culturing them and their short life span. Eggs are deposited by the adults on the surface of the soft food on which the larvae will feed. The eggs hatch and the maggot-like larvae begin to feed. The larvae transform into puparia while adhering to some relatively dry surface near the food source. A few days later the adult flies emerge, at first light in color but on exposure to air, the color darkens. The life cycle can be completed in 10 days when temperatures are in the mid to upper 70's; at 68°F it may take 15 days.

Mayflies are soft-bodied, slender insects that may be seen flying in great clouds moving across streams and lakes at twilight in an up-and-down-motion mating dance. Fishermen model many "dry flies" after these fragile insects. The adults have two or three long tail filaments and may be seen when attracted to lights in the early evening. Generally the adults hide in trees and shrubs close to aquatic areas until the mating flight. Hundreds of these insects move off the vegetation and into the air, fly about 1/2 hour during which time some of them mate, and then return to vegetation for cover or to the surface of the water to lay eggs. The nymphs live in clear fresh waters and feed on vegetable matter, including diatoms and desmids (which make the gold-green color upon stones of the brook bottom). They will also feed on soft tissues of larger plants, either alive or dead.

Drain flies, also called filter flies, moth flies, and sewage gnats, are nuisance pests. We are most concerned with these flies when they appear in our houses or buildings, creating annoyance. The larvae breed in moist organic matter and feed principally on algae. The muck of gelatinous material that accumulates on the sides of drains and overflow pipes in houses may provide suitable breeding sites. Some species are able to survive hot water and soap. Where they are a problem, the adult flies may be seen resting on walls in kitchens, bathrooms and basements. Usually only a few are present at any one time; some die off, and others emerge, but occasionally, they may occur in large numbers.

The adults are small, thickly haired, broad-bodied flies, usually less than 5 mm (1/4 inch) in length. The wings are often clothed with hairs or scales, giving the flies a "fuzzy" appearance. Wings are held roof-like or tent-like over the body when at rest. They are not strong fliers and often move by crawling on the walls or other surfaces. When they do fly, they move only a few feet at a time and fly in a jerky line. The adults may be attracted to lights at night. Outdoors, these flies are common in shady places in the vicinity of water, and they are often found in large numbers on dense foliage in swampland.

Drain flies may go through the life cycle in 1 to 3 weeks, and the adults can live for about 2 weeks after emerging. Eggs are laid in irregular masses in such places as water traps in plumbing fixtures, around built in sinks, garbage disposals, or anywhere moist decaying organic matter occurs. The larvae and pupae are aquatic or semi-aquatic, living in the decomposing film of organic matter.