Stable flies typically target the lower legs of livestock when feeding, often clustering around the front legs where they are easiest to spot. In fact, monitoring stable fly pressure can be done by counting the number of flies on an animal’s front legs—economic losses can begin when as few as two flies per leg are observed. At higher infestation levels (more than 25 flies per leg), the flies spread to the animals' flanks and undersides. These pests are persistent, intermittent feeders, returning multiple times throughout the day for brief feeding sessions lasting 2 to 5 minutes. Despite the painful nature of their bites, stable flies are largely undeterred by animals’ defensive behaviors such as stamping, swishing, or swatting.

The damage caused by Stomoxys species goes far beyond irritation. Their constant biting leads to chronic stress and blood loss in livestock, weakening animals and in some cases contributing to anemia. Affected animals often reduce their feed intake as they prioritize avoidance behaviors—such as bunching together or pacing—over grazing or resting. This behavioral shift leads to reduced weight gain, milk production, and overall productivity. Open feeding wounds from repeated bites can also become entry points for secondary infections. Additionally, the flies can trigger overheating in animals that cluster together to avoid bites, especially under high temperatures. From a health perspective, stable flies are also known mechanical vectors of various pathogens, including bacteria like Bacillus anthracis (anthrax), Leptospira spp., and Anaplasma spp.; viruses such as equine infectious anemia (EIA) and hog cholera; and protozoa like Trypanosoma evansi, which causes surra. This makes them not only a welfare issue, but a serious biosecurity concern on livestock operations.

Adult stable flies (Stomoxys spp.) are between 5–7 mm in length and closely resemble house flies in overall shape, including the presence of four dark stripes on the thorax. However, they can be distinguished by several key features: they are lighter grey in color, have a broader abdomen marked with a distinctive “checkerboard” pattern of dark spots, and possess long, piercing proboscises that extend forward from the head—specialized for blood feeding. Another behavioral clue is their typical resting posture: stable flies often settle on vertical surfaces with their heads pointed upward. Like house flies, females tend to be larger than males and have more widely spaced eyes.

Female stable flies require a blood meal prior to each egg-laying cycle and typically do not lay eggs until after their third blood meal—averaging four feedings before their first oviposition. Once mated, females lay small (~1 mm), white, sausage-shaped eggs, either singly or in small groups of 25–30. Preferred oviposition sites are moist, decaying organic materials rich in microbial activity, such as compost heaps, rotting hay, silage edges, or spilled feed. Under suitable temperature and humidity conditions, yellowish-white maggots hatch within 1 to 4 days. These larvae grow through three instar stages, reaching 5–12 mm in length, over a period of 10–30 days depending on environmental conditions. Notably, larvae can survive through winter in livestock housing, posing a challenge for year-round fly management.

After completing the larval stages, mature maggots migrate to drier areas nearby and pupate within reddish-brown cases measuring 4–7 mm long. Adult flies emerge in 6 to 20 days, depending on temperature. In warm summer conditions, the full life cycle—from egg to adult—can be completed in as little as 3 to 4 weeks, enabling stable flies to multiply rapidly if not properly managed.

Preventing stable fly (Stomoxys spp.) infestations requires a proactive, multi-layered approach focused on sanitation, habitat disruption, and early monitoring. Since stable flies lay their eggs in moist, decaying organic matter—such as rotting hay, spilled feed, wet bedding, manure mixed with straw, and edges of silage pits—eliminating these breeding sites is the first and most critical step. Regular cleaning of animal pens, prompt removal of spoiled hay and feed, and proper storage of silage and compost can significantly reduce the conditions needed for stable fly development. Pay particular attention to shaded, humid areas where organic material tends to accumulate and remain undisturbed.

To monitor and assess fly activity, especially before populations reach economic thresholds, yellow sticky cards like Koppert’s Horiver traps can be used strategically around barns, feedlots, and silage bunkers. These cards help detect early adult fly presence and can guide timely interventions. Sticky roller tape can also be placed in high-traffic fly zones to passively trap adult flies. While these tools won't eliminate infestations on their own, they play a vital role in fly surveillance and suppression.

Additionally, ensuring good drainage and minimizing moisture buildup in and around livestock housing is essential. Wet zones under waterers, in corners, or where feed waste collects are prime breeding sites for stable flies. In outdoor settings, rotating bale feeders and breaking up trampled hay and manure mats can help dry out the environment and interrupt fly development. When used together with biological or physical controls, these prevention strategies help maintain stable fly populations at manageable levels, protecting animal welfare, farm productivity, and public comfort.

Biological control can play a valuable role in managing stable fly (Stomoxys calcitrans) populations, particularly in settings where chemical controls are limited or undesirable. Since stable flies develop in moist, decaying organic matter, introducing natural enemies that target the immature stages—especially pupae—can significantly reduce the emergence of biting adults over time.

Koppert’s BioPar, which contains the parasitic wasp Muscidifurax raptorellus, is one such tool. These tiny, non-stinging wasps actively search for the pupae of manure- and compost-breeding flies, including stable flies, and lay their eggs inside. The developing wasp larva consumes the fly pupa from within, preventing adult emergence. Releasing BioPar regularly during the fly season—especially in areas where moist organic waste builds up, such as around feed bunks, silage pits, bedding areas, and compost piles—helps suppress future generations of stable flies.

Although stable flies are more mobile and aggressive than many other nuisance flies, targeting their development sites with parasitic wasps is a reliable way to reduce overall pressure. For best results, biocontrol should be used in conjunction with strong sanitation practices and regular monitoring (using tools like sticky cards or tape). This integrated approach limits breeding opportunities, reduces the number of flies reaching adulthood, and provides long-term relief from the stress and health risks stable flies pose to livestock and workers.