INTRODUCTION.
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.
RECOGNITION.
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.
SIMILAR GROUPS.
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.
House fly, Musca domestics, with wing's 4th longitudinal vein sharply
bent forward near tip, mouthparts retractile, sponging.
Flesh flies (Sarcophagidae) with wing's 4th longitudinal vein sharply
bent forward near tip, mouthparts sponging, tip of abdomen pink.
BIOLOGY.
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.
HABITS.
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.
