Stable Fly

The stable fly, Stomoxys calcitrans, is a cosmopolitan species closely related to the house fly and nearly indistinguishable from it at a glance. The key difference lies in its mouthparts: while house flies have a soft, sponging proboscis for lapping liquids, stable flies possess a rigid, bayonet-like proboscis adapted for piercing skin to feed on blood.

Both male and female stable flies feed on blood, making them a persistent biting nuisance around livestock operations, stables, and beaches where organic debris accumulates. Their bite is typically delivered quickly, often around the legs of a host.

Stable flies breed in moist, decaying organic matter rather than fresh manure alone, and are frequently associated with soiled bedding, grass clippings, and rotting seaweed along shorelines.

• Gray thorax marked with four dark longitudinal stripes
• Checkered gray-and-black pattern on the abdomen with dark spots
• Rigid, slender proboscis projecting forward from the head, visible without magnification
• Body size similar to a house fly, 6-8 mm long
• Lookalikes: house flies appear nearly identical but have a soft sponging mouthpart rather than a piercing proboscis and do not bite

Stable flies are found worldwide in temperate and tropical regions. They breed in moist, decaying organic matter such as soiled livestock bedding, grass clippings, compost, and rotting seaweed on beaches, and are especially common around stables, barns, pastures, and coastal areas with wrack lines.

Both sexes require blood meals and typically bite the legs of livestock, pets, and humans, delivering a quick, sharp bite before moving on. Between feedings, stable flies rest on fences, walls, and other surfaces near their breeding sites. They occasionally supplement their diet with plant sugars but rely primarily on blood for reproduction.

Females lay batches of eggs in moist, decaying organic material such as soiled bedding or rotting vegetation. Larvae develop through three instars while feeding within this material, then move to slightly drier surrounding substrate to pupate. In warm weather, the complete cycle from egg to adult takes roughly two to four weeks, with multiple overlapping generations produced through the warm season and larvae or pupae overwintering in temperate climates.