Stable Fly

Common Name: Stable Fly
Scientific name: Stomoxys calcitrans

Introduction. This fly receives its common name from its close association with stabled 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 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.

Recognition. Adults measure 1/4 to 3/8 inch long and are dull gray with 4 black longitudinal stripes on the thorax. The piercing mouth parts (proboscis) project forward from beneath the head. When resting, the stable fly squats with its head cocked up and abdomen touching the resting surface.
Similar Groups. (1) The house fly, Musca domestica, has sponging mouth parts that are not visible from above. (2) Flesh flies (Sarcophagidae) only have 3 stripes on the thorax. The tip of abdomen is orange-red colored.

Biology. Adult females lay their eggs (average 376, range 200 to 632) scattered throughout an acceptable larval food such as damp straw contaminated with urine and feces, piles of lawn clippings, rotting fruit and vegetables, and decaying hay, grass or seaweed (piles of aquatic algae on beaches). In warm weather eggs hatch after 23 hours and the 3 larval instars require 9 days total. Pupation requires 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. 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 also can cause a 40 to 60% reduction in milk production. 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.

Cultural Control & Preventative Measures. Stable flies infrequently enter structures but may do so in numbers. Exclusion is the only practical method of control. Light traps strategically located inside can help reduce the flies once inside and are recommended in areas with large stable fly populations.
To decrease breeding sites, breeding materials must be disposed of properly and on a timely basis, which is at least once every 2 weeks because stable fly developmental time is about 15 days. For example, the proper management of grass clippings is especially important on golf courses. For urban and backyard stables, bedding and hay in the field contaminated with feces and urine must be disposed of on a timely basis. Also, along beaches the accumulated washed-up vegetation should be removed on a regular and timely basis.

Professional Control. Outside, the application of appropriately labeled residual insecticides to resting surfaces on structures can help reduce the immediate problem. Rottler Pest Management professionals can recommend and install the appropriate type and number of insect light traps to help alleviate stable fly problems in and around structures. Insecticide-treated fly perches and traps may prove helpful in reducing populations of stable flies, if placed strategically on the premises.