The stable fly and house fly are the major insect pests at confined livestock units. The stable fly has a piercing-type mouthpart which is used to pierce the skin to obtain a blood meal. House flies do not bite because they have a sponging-type mouthpart, with which they feed on semiliquid material. The life cycles of the two species are similar, consisting of eggs, larvae (maggots), pupae, and adult. During summer months the stable fly completes its life cycle in about 3 weeks. The house fly requires about 2 weeks, or, in southern areas as little as 9 or 10 days. Both species deposit eggs in wet decaying organic matter. This includes spilled livestock feed and manure mixed with soil and moisture. In addition, the house fly will breed in fresh manure. The two species generally overwinter as slowly developing larvae in breeding areas below the frost line. The house fly may breed during the winter in warm buildings if breeding material is present.
Cattle under attack by stable flies will bunch together with each animal attempting to find a position within the bunch which protects their front legs—the favored feeding site of the flies. Considerable energy is expended by foot stomping, tail switching, and throwing the head toward the front legs in an effort to dislodge the flies or prevent feeding.
Stable flies reduce weight gains, milk production, and feed efficiency—both from their feeding and because of the bunching behavior of the cattle, which may induce or increase heat stress. House flies have not been shown to reduce animal weight gain and feed efficiency, but are known to transmit several animal diseases. The disease organisms recovered from house flies range from viruses to nematodes. The most common of these are the bacteria associated with enteric infections. The house fly mouthparts and feeding habits (filth sources) make it efficient in transmitting bacterial and viral agents. Over one hundred different disease organisms have been recovered from house flies, and the fly has been implicated in the transmission of 65 of these. Transmission may simply involve the mechanical transfer of the disease agent, from the mouthparts or body of the fly, to the animal host. In other cases, the disease agent may multiply in the fly and be transmitted after populations of the disease agent build up to high numbers, or it changes to a different life stage.
One other important economic factor associated with stable flies and house flies is the threat of nuisance lawsuits. Generally odor, dust, and flies are cited together as constituting a nuisance by the plaintiffs. The lawsuit may seek damages or, perhaps worse, request closing of the livestock facility.