Stable Fly

This fly receives its common name from its close association with stabled domestic animals; they are also sometimes called biting houseflies because of their similar appearance, and beach flies because of their abundance in beach areas. Stable flies are a pest because of the painful bit they inflict. They are primarily a problem in suburban and rural areas where horses and other livestock are stabled and in beach areas. They are worldwide in distribution and found throughout the United States, especially in the grain belt in the central states from Texas to Canada.

Recognition

Adults about 1/4-3/8" long. Color dull gray with 4 black dorsal longitudinal stripes on thorax, with middle 2 stripes separated by a prominent pale area, and abdomen with nearly round dark areas. Head with proboscis/beak stiff, nonretractile, projection forward forms lower part of head. Antenna 3-segmented, 2nd segment with longitudinal suture, 3rd segment with bristle toward 3rd vein but not angled, with 2 posterior cells, and wings held widely apart at rest. When resting, squats with head cocked up and abdomen touching resting surface.

Mature larva about 3/8-1/2" long, eyeless, legless, and tapering towards head from large rounded rear segment, head represented by 1 pair of dark hooks. Color cream but with greasy appearance. Posterior spiracles slightly raised. Spiracular area smooth and entirely dark, with 3 S-shaped spriacular openings, and with an indistinct donut-shaped structure in its center.

Habits

Adults may take blood meals more than one each day but also feed on sugar sources. Although peak feeding occurs in the early morning and late afternoon on hot days, biting is diminished on cloudy and/or windy days. Stable flies are being referred to in the common expression "It must be going to rain, the flies are biting." They attack the ankles of humans and the belly, and lower body of livestock, particularly horses and cattle. They not only agitate livestock but also can cause a 40-60% reduction in milk production.

Larvae breed in a variety of moist situations but the material must be loose and porous. Favorite materials include animal bedding and old rolled hay in the field which are contaminated with urine and feces, just fermenting grain, straw stacks, piles of grass clippings especially from golf courses, grass clipping clods stuck on the underside of lawn mowers, and rotting fruits and vegetables such as onions, cabbage, celery strippings, and peanut litter left in the field, and spilled silage in fields. Just fermenting beach grasses and seaweed are very poor breeding sites.