Riley Pest Management
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source for information on flies

Stable Fly   Stomoxys calcitrans

Stable flies posses one of the fiercest bites of any common fly species. Unlike the nearly painless bite of the mosquito and other biting flies, stable flies are equipped with scissor-like mandibles that tear flesh. While male stable flies feed on pollen and are important pollinators, females feed on blood in order to assist in egg development.

The peak of stable fly season coincides with warm weather and these flies are most active in summer and early fall. They prefer wet areas, congregating most commonly near the shores of lakes and at beaches. Horse flies are attracted to dark objects and use their complex, compound eyes to locate prey. Stable flies appear to be attracted to certain odors, as well as to carbon dioxide. Female stable flies lay eggs on rocks and plants near water. Larvae then prey on invertebrates such as snails and grubs, which they find by burrowing into the soil.

Stable flies are similar in appearance to house flies; however stable flies have a bayonet-like mouthpart protruding from the front of the head, and they lack the four dark stripes on their thorax that are indicative of house flies. They are brownish-gray in color and the abdomen has a checkered appearance.


Approximately 1/4-inch long.

The Stable fly is a blood-sucking fly that is of considerable importance to livestock, pets, and people. When hungry, Stable flies are very persistent and can inflict a painful bite on both animals and humans. They can even affect the tourism industry in Florida, especially in Western regions. If stable flies are numerous at state fairs, for instance, their bites and annoying presence can drive visitors away and make them unlikely to return.

Both sexes of stable flies feed several times per day, usually on a drop or two of blood at a time. They prefer feeding on the legs and lower body of livestock. If left undisturbed, they can become fully engorged with blood in less than five minutes. Stable flies breed in piles of moist, decaying plant material, such as grass clippings and hay, especially when mixed with animal manure and urine. Backyard compost and piles of grass clippings are also ideal breeding sites for stable fly larvae.

Each female fly may lay 500 to 600 eggs in 4 separate batches. They typically hatch in 2 to 5 days into larvae which feed and mature in 14 to 26 days. The maggots transform into small reddish-brown pupae from which the adult flies emerge. The average life cycle is typically three to four weeks.

Adult stable flies are common around barns, animal pens, and often bite while cattle are resting in the shade of a building or under a tree. Although they have always been known only as a pest of cattle housed in barns, it is becoming a pasture pest in situations where large bales of hay are used. This is due to larval development takes place in the damp, rotting hay at the base of improperly stored bales.

Stable flies also congregate on beaches as they are sensitive to wind; they sometimes may even breed in damp seaweed. Some fly to boats where they continue to bite even when taken offshore. They are most common during the morning hours, when the wind is from the north. They usually are not common in residential areas.

Economic/Health Concerns:
The stable fly is the most common biting fly pest of confined livestock. Its irritating bites can cause considerable distress to animals and result in reduced production. Heavy infestations of more than 50 flies per animal can reduce weight gain by 25 percent and milk production by 40-60 percent. The stamping of feet is usually a sign that stable flies are present and feeding. Livestock have also been known to stand in water up to their necks to escape biting flies during heavy infestations.

Stable flies are also known to transmit diseases such as anthrax, Equine Infectious Anemia (EIA) and anaplasmosis to animals. Since they leave an animal immediately after feeding, they often go unnoticed unless heavy outbreaks occur. Bite wounds can also become sites for secondary infection.

As with other fly species eradication methods, the first step that should be taken is to remove or reduce breeding sites. Management of livestock waste should take place as often as possible, since the stable fly can complete its life cycle in as little as 21 days. Piles of fresh manure should removed or spread to dry.

Also, never allow wet straw to pile up in or near buildings. Since straw is one of the most common breeding grounds, it is not recommended for livestock bedding. Stable flies can also be controlled using sticky traps or those that have an electrocuting grid. One trap should be used for every 30 feet of wall space.

"Riley Pest Management is a small company with a big heart that will go the extra mile to take care of an issue for you no matter when it happens. They have proven to be a very good friend to non-profits."

-- Duggan Cooley, former CEO- RCS

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