Stomoxys calcitrans
stable fly

Stomoxys calcitrans is a cosmopolitan insect, meaning that it can be found worldwide as long as suitable food and weather conditions can be met.

The habitat of the stable fly, as suggested by its common name, is almost anywhere that horses, cattle, and other agricultural animals can be found (especially inside barns and stables). ()

The stable fly closely resembles the common housefly (Musca domestica). Unlike the common housefly, Stomoxys calcitrans have a broader abdomen. Adult stable flies average 8 mm in length, have a gray body, and can be identified by four characteristic longitudinal stripes across the thorax as well as several dark spots on top of the abdomen. On the vertex and frons there are three ocelli and two large compound eyes. Sexual dimorphism occurs in this species, and there is more distance between the compound eyes in females. The proboscis of the stable fly is black, long, and thin, protruding from the front of the head. Its other mouthparts are modified, with the labellum having rows of teeth in order to pierce the skin of its host. The palps are one third of the length of the proboscis.

Larvae range in size from 5 to 12 mm long. Mature larvae are yellowish white maggots, and are a cylindrical shape that tapers anteriorly.. The pupae have a reddish-to-dark brown exterior and are 4 to 7 mm long. The posterior spiracles on the puparia are black with three S-shaped yellow slits, and are lightly sclerotized. ()

Stomoxys calcitrans eggs take one to four days to develop. The length of this period is affected by temperature, humidity, and how long the egg was retained by the female. The larval stage lasts from 11 to 30 (and sometimes more) days, based upon habitat suitability and availability of food. After the third instar (growth stage) the maggot will pupate for 6 to 20 days. As with larval maturation, length of pupation is based upon food abundance and quality during larval growth. ()

Soon after mating males die. Females die soon after laying their eggs.

Stomoxys calcitrans locates its host by sight. On cattle it will first land and rest on the back of the animal. As soon as it is disturbed, it flies to the outside of the forelegs; where it will bite the cow near the knees and begin feeding. On horses S. calcitrans prefers feeding on the sides of the neck, lower legs, and underbelly. After feeding, S. calcitrans rests nearby, usually on warm, sunny sites such as fences, walls and vegetation near the hosts. When disturbed it will fly and then return to the original spot of feeding. ()

These flies have good eyesight and communicate visually.

Stomoxys calcitrans is a daytime feeder. The adults of both sexes feed on blood. There is low host specificity; although they feed mainly on the blood of cattle and horses. Adults locate a host by sight, and feeding is usually completed in two to five minutes. After feeding the stable fly is sluggish, and remains motionless near the host. The stable fly will generally feed from many hosts before it is replete. Studies show that there is a rise in feeding during warm wether, whereas there is a decrease in feeding rates during rain. After hatching, the larvae begin feeding on local microbial flora and fauna. ()

There is little known predation of this species.

Stomoxys calcitrans economically affects humans in two ways: livestock reduction and disease. The accumulation of stable fly bites leads to a certain degree of anemia, weight loss in cattle, reduced milk production in dairy cattle. In this way, S. calcitrans costs the US millions of dollars. It also affects the cattle industry by destroying the hides of cattle due to the holes created by the piercing of the skin for feeding.

Studies have shown that as few as 20 flies per animal can reduce the rate of milk production. The effect on the hosts increases proportionally with an increase in the number of bites. This trend eventually reaches a plateau, due to the fact that the stable fly is only a daytime feeder.

For ox, horses, and sheep, S. calcitrans is a vector of Trypansoma cazalboui. This parasite causes the disease known as souma. For ox, it is a vector of T. pecaudia. For domestic animals and humans it is a vector of anthrax. This disease can cause a number of different symptoms, inculding lesions in the lungs and brain. It is also a vector for T. evansi (the agent of Surra), T. brucei, ERF, brucellosis, swine erysipelcs, equine swamp fever, African horse sickness, and fowl pox. ()

There is no obvious human benefit provided by these flies.

This species has large populations world-wide, and is in no danger of extinction.

This species was introduced to North America in the 1700's. ()