Egg -- Eggs of both species are white, narrow, elongate and slightly flattened and are 2 mm long. They have wing-like processes which enable them to float in liquids.
Larva -- Fannia maggots have many dorsal and lateral projections and develop through three instars. About 1.5 mm long when newly hatched, the first instar of the little house fly larva is white with only the tip of its mouth hooks black. The second instar is about 3 mm long at first and has a little more black coloration. When mature, the larva has a 5 to 8 mm long, light brown body with an entirely black head.
Pupa -- Slightly smaller than mature larvae, the pupae of lesser house flies develop inside the darkened, hardened skins (puparia) of the last larval instar.
Feeding Habits -- Adult flies feed on various liquids and are often attracted to aphid-infested plants by the presence of honeydew (a sweet, sticky aphid excretion). Larvae typically consume decaying organic matter and excrement but have been known to parasitize the intestinal tract of man and animals. In some areas, lesser house fly larvae are the predominant maggots breeding in chicken manure.
Damage -- Fannia spp. Flies are primarily an annoyance. Like common house flies, little house flies breed in garbage and manure and may transfer disease-causing organisms to human food such as dysentery bacilli. In addition, larvae of this species have been known to develop within the intestines of man and animals (intestinal myiasis). The coastal fly, however, has not been implicated as a disease vector or an agent of myiasis.
Life History -- Adult flies often take refuge in warm rooms and stables during winter. In mild climates, this species may overwinter as larvae, prepupae, or pupae. During severe winters, however, only pupae survive. Overwintering adults often become active by late February, but emergence of new flies from overwintering pupae usually does not occur before mid-March.
Two to 5 days after emerging, female flies begin depositing eggs on the surface of moist, decaying substrates. Eggs incubate only 1.5 to 2 days before larvae hatch. These maggots feed and develop for 7 to 10 days. Within 9 to 14 days, a new generation of flies emerges and the life cycle is repeated. Though detailed outdoor studies have not been carried out, results of lab experiments suggest that as many as seven successive generations occur each year.
Adults of this genus may live as long as two months. Populations flourish during cool seasons, particularly spring, early summer, and late fall. Peak numbers usually occur by July after which dry, hot weather and parasitism causes populations to subside until fall. Lesser house fly maggots are often common in poultry and livestock manure.