**Stable Flies** (*Stomoxys calcitrans*) are biting flies that closely resemble the common house fly, but unlike the house fly, they are hematophagous (blood-feeding). They are a significant **agricultural and livestock pest** globally. The conflict is severe: they inflict painful bites on humans and animals, and their persistent biting causes **intense stress, reduced weight gain, and lower milk production** in cattle. They are also known to be mechanical vectors for several livestock diseases.
Taxonomy and Classification
Stable Flies belong to the order Diptera (Flies). They undergo complete metamorphosis. Both male and female stable flies feed on blood (unlike mosquitoes, where only the female bites). They are commonly found around livestock, but can also be nuisance pests in beach communities and resorts (“beach flies”).
Physical Description
Adult Stable Flies are 1/4 to 3/8 inch long.
- **Appearance (Key ID):** Grayish body, similar to the house fly, but with a distinctive, forward-projecting, stiff **bayonet-like proboscis** used for piercing and sucking blood. The abdomen has four dark, rounded spots.
- **Biting Behavior (Key ID):** Often found biting the **lower legs and ankles** of humans, or the lower legs and flanks of livestock. They are persistent and difficult to shoo away.
- **Breeding Habitat:** Decaying organic matter mixed with moisture, such as spoiled hay, grass clippings, silage runoff, and wet manure/straw mixtures.
- **Conflict:** Painful bites and massive economic loss in livestock production.
Distribution and Habitat
Stable Flies are cosmopolitan. Their habitat is livestock facilities, dairies, horse stables, and any area with wet, decaying vegetation or manure, as this is where the larvae develop.
Behavior and Conflict
The conflict is primarily economic and stress-related.
- **Economic Impact:** The pain from the bites forces cattle to bunch together, stomp, and stop feeding, leading to reduced feed efficiency, lower milk production, and decreased weight gain.
- **Painful Bite:** Unlike the soft mouthparts of the house fly, the stable fly’s proboscis is designed to slice skin and capillaries, resulting in a sharp, noticeable bite.
- **Vectoring:** They mechanically transmit pathogens like the bacteria that cause anthrax and the virus for equine infectious anemia (EIA).
Management and Prevention
Control is integrated pest management (IPM), centered on eliminating breeding material (source reduction).
- **Sanitation:** The single most important control: remove and spread out all wet, decaying hay, silage, manure, and grass clippings weekly to allow them to dry out, eliminating the larval habitat.
- Release commercially available parasitic wasps (*Spalangia* species) that parasitize the stable fly pupae in the breeding material.
- Use walk-through traps or sticky traps in barns to catch adult flies.
- Apply residual insecticides to the outside surfaces of stables and barns where the adult flies rest.
Conservation and Research
Stable Flies are managed as high-priority livestock and public health pests. Research focuses on improving environmental sanitation methods, optimizing parasitic wasp releases, and understanding fly resistance to chemical controls.