The Stable Fly

Common Name:
Stable Flies
Scientific Name:
Stomoxys calcitrans (Linnaeus)


This fly receives its common name from its close association with stabeled domestic animals; they are also sometimes called biting house flies because of their similar appearance, and beach flies because of their abundance in beach areas. Stable flies are a pest because of the painful bite they inflict. They are primarily a problem in surburban 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.


Adults about 1/4-3/8" (7-8 mm) 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 proboscislbeak stiff, non- retractile, projecting forward from lower part of head. Antennae 3-segmented, 2nd segment with a longitudinal suture (impressed line), 3rd segment with bristle (arista) having hairs only on dorsal side. Wing with 4th longitudinal vein curved forward towards Srd 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" (8-11 mm) 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 (breathing pores) slightly raised, spiracular area smooth and entirely dark, with 3 S-shaped (sinuous) spiracular openings/slits, and with an indistinct donut-shaped structure (button) in its center.


  1. False stable fly, Muscina stabutans and the fly Muscina assimilis with mouthparts retractile, sponging, tip of scutellum (rear end of thorax) more or less pale, and false stable fly stands erect when resting.

  2. House fly, Musca domestics, with wing's 4th longitudinal vein sharply bent forward near tip, mouthparts retractile, sponging.

  3. Flesh flies (Sarcophagidae) with wing's 4th longitudinal vein sharply bent forward near tip, mouthparts sponging, tip of abdomen pink.


Adult females lay their eggs (average 376, range 200-632) scattered throughout an acceptable larval food such as straw contaminated with urine and feces, piles of lawn clippings, rotting fruit and vegetables, and decaying grass or seaweed. At 84'F (26.7'C) and about 50% RH, eggs hatch after 23 hours, the 3 larval instars require 23 hours, 27 hours, and about 7 days respectively. Pupation occurs in the drier areas with the pupal stage requiring about 5 days, the first adults appear at about 15 days with peak emergence at about 18 days, and the first egg laying occurs at about 22 days after the original eggs were laid. Adults of both sexes feed on blood and may do so more than once each day with peak feeding occurring in the early morning and late afternoon. During a simple feeding, which lasts 1.5-8 minutes, adults often puncture the skin several times before drawing blood and will take in an average of 3 times their weight in blood. Females mate once. Adults live about 20 days during hot summer weather. They overwinter as larvae and/or pupae.

Stable flies act as both biological and mechanical vectors of disease organisms. Fortunately in the U.S., stable flies are only involved with the transmission of livestock disease pathogens.


Adults may take blood meals more than once 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, lower body, and limbs of livestock, particularly horses and cattle. They not only agitate livestock but 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 (straw) and old rolled hay in the field which are contaminated with urine and feces, just fermenting grain straw, straw stacks (especially oat straw), 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, waste celery strippings, and peanut lifter left in the field, and spilled silage in fields. Just fermenting beach grasses and seaweed are very poor breeding sites. Adults are attracted to dark colors and people wearing dark clothes are often attacked. Their favored resting sites are sunny fences, walls of structures, and painted surfaces in general. If the flies are disturbed, they tend to return to the same spot. At dark, stable flies seek sheltered areas and cease biting.