Stable Flies 

Stable flies (Stomoxys calcitrans), known for their painful bites using piercing mouthparts, require blood to reproduce. This causes significant discomfort to cattle and, when populations are high, can reduce milk production in dairy cows, weight gains in calves and beef cattle. Both female and male stable flies feed on blood once or twice a day, typically targeting the legs of the cattle. However, when populations are high, they will feed on other parts of the animal as well.

Cattle under attack from large numbers of stable flies often show signs of distress, such as vigorously stomping their legs to dislodge the flies, which further impacts their feeding time, weight gains and milk production. Stable flies can infest cattle in both barns and pastures.

This video shows cattle moderately stomping off stable flies

Stable flies deposit their eggs in decomposing organic material and thrive in environments containing rotting moist grass, hay, straw, manure, and silage. They also lay eggs in lake weeds accumulating on banks, and any other decomposing materials leading to significant infestations, and can migrate long distances to find livestock.

A single female stable fly can lay up to 400 eggs and survive for about a month. Under optimal warm conditions, their lifecycle spans approximately 21 days from egg to adult. Once emerging as adults, they can take a blood meal within 12 hours.

Action Threshold

The action threshold for stable flies is a cumulative count of 10 flies on all four legs of an animal. Observing and counting flies on at least 10 to 15 cattle, then calculating the average, helps determine if intervention is necessary.

Management of Stable Flies

Sanitation: Proper sanitation is crucial for controlling stable flies. They lay eggs in moist, decaying organic matter. Breaking their lifecycle by regular cleaning is essential. Clean all moist organic matter from every corner of the barn, including stalls, calf hutches, pens, maternity areas, sick cow pens, under feeders, manure handling areas, and storage areas for feed, silage, and hay. Even a small amount of moist organic matter can produce hundreds of flies.

Composting: Composting manure, feed, old silage, hay, and bedding materials can kill fly eggs, maggots, and pupae. Compost piles reaching 120 degrees or more can effectively eliminate these stages of the fly. Turning the compost pile weekly prevents reinfestation by flies.

Spreading Manure and Bedding: Spreading manure, old bedding, silage, hay, and feed on a field in a thin layer allows the material to dry out, killing fly eggs and maggots in the decomposing organic matter.

Bedding Types: The type of bedding used can impact fly control. Moist straw mixed with manure, silage, hay, and feed is ideal for fly reproduction. Alternatives like sand, gravel, wood shavings, wood chips, and sawdust have lower fly reproduction rates. Nonetheless, regular cleaning of manure, feed, silage, and hay from stalls and pens is necessary.

Placement of Feed and Water: Placing feed and water outside of calf hutches, pens, and free-stall areas prevents contamination of bedding, reducing the risk of flies laying eggs.

Water Control: Preventing water from contacting bedding, hay, or feed is essential. Position waterers to avoid spillage, ensure proper drainage around barns, and direct rainwater away from buildings and feed storage areas. For calf hutches, mound gravel to ensure proper drainage and prevent moisture build-up. Adequate ventilation and dry conditions in calf hutches are also crucial.

Bedded Packs: For producers using bedded packs, it is essential to keep the area dry and add fresh bedding material regularly. Properly maintained bedded packs can minimize fly production.

Clean Hay/Haylage Feeders on Pastures: Stable flies breed in areas where hay or haylage accumulates on pasture. Clean these areas weekly to prevent significant fly production.

Biocontrol: One type of natural predator of fly pests is parasitoid wasps, which may already be present on farms. To enhance their impact, additional parasitoids can be purchased and released. By strategically releasing specific parasitoids in barn areas, the wasps act like “smart bombs” and target stable fly pupae.

For comprehensive insights into parasitoids targeting house and stable flies, please explore the following website: https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/fact-sheets/muscidifurax-raptor-and-m-raptorellus-biocontrol-agent-fact-sheet

Organic Solutions

For organic producers, approved forms of pyrethrum or neem and other natural repellents can offer some relief, though their efficacy may be limited to short durations.

Insecticidal Measures

Residual insecticides can be applied to barn walls to control stable fly populations. Flies resting on treated surfaces will be exposed to the insecticide. Various insecticidal products can also be applied directly to cattle to reduce fly pressure. VetPestX is a valuable resource for selecting suitable insecticides tailored to specific pasture conditions. More information can be found at VetPestX.