Length: Adult stable flies are 5-7 mm long
Thorax: Dark-grey in colour with 4 black stripes
Abdomen: Grey with black spots forming a checkerboard pattern
Eyes: Female: Widely separated by an ovoid frontal stripe
Male: Separated by a narrow frontal stripe
Larvae: Mature larvae are over 10 mm long, smooth and pale yellow to creamy white
The most obvious difference to house flies is that the stable fly has a protruding biting mouthpart (Figure 1).
Figure 1 A stable fly left, and a house fly right showing their different mouthparts. Image courtesy of the Peter Green, Queensland Department of Agriculture and Fisheries.
The life cycle of the stable fly has four stages: egg, larva, pupa and adult. Each female lays over 500 eggs during her lifetime in scattered groups of 15-20 in rotting, spoiled or fermenting organic matter. The addition of animal manure, moisture, soil and straw, hay, silage or grain makes an ideal medium for stable fly development. Cattle feedlots and dairies provide ideal fly breeding media.
Larvae develop over 7-10 days in ideal conditions, but in low temperatures (15˚C) this can increase to more than 7 weeks. When finished with feeding, the larvae then move to a drier area to form a dark brown protective pupal case around the developing fly. After a few days the adult fly breaks out of this pupal case and searches for a host to feed on its blood.
Stable flies will bite and feed on any warm-blooded animal, though they have a higher preference for cattle and horses. They penetrate the animal's skin with their piercing mouthpart, with both moth male and female flies feeding on blood twice per day, each time sucking up around 26 mg (0.02 ml) of blood.
Female flies mate 1 day after emergence, and after 5 days of blood feeding they are ready to lay eggs and the cycle starts again.
In summer most adult stable flies live only 1-2 weeks, whereas in cooler months they will survive up to 6 weeks.
Adult stable flies are often seen resting on vertical surfaces such as fence posts and railings and are often seen on the sides of white vehicles. Stable fly larvae grow in rotting grass/hay and in areas with old manure, especially when mixed with vegetable matter.
In cattle feedlots larvae can be found in high numbers in drains, sedimentation ponds, and the hospital/induction areas. Additional areas larvae grow in include under fence lines where water has kept manure moist, silage pits, and in spilled grain and feed that has started to rot and ferment.
In paddocks stable flies breed in rotting hay residues around feeders and in yards where bales are fed out to cattle. Vegetables and fruit used as supplementary feed that have rotted on the ground also provide an ideal medium for larval growth.
Stable flies typically bite the legs and belly areas of cattle. The normal reaction to stable fly biting is stomping of feet, head tossing and switching of tail. Research has shown a strong correlation between the number of leg stomps and numbers of stable flies. Also see assess fly numbers.
In paddocks, some other avoidance behaviors include standing in water, lying down with their legs tucked underneath their body, flicking sand on themselves and bunching or crowding together. When cattle bunch up to repel flies this can lead to additional problems such as heat stress and reduced feeding.
Adult stable flies have significant medical and economic impacts through annoyance, production losses and potential disease transmission between animals and as few as 20 adult stable flies per animal can reduce daily weight gain and milk production.
For more information on stable fly treatment and management see the following links.
Management of situations within livestock production where stable fly breeding can occur are addressed in the Biosecurity and Agriculture Management (Stable Fly) Plan 2016 under which Stable Fly is a Declared Pest.
10. Keeping stock