Close Up of Flies

Did you know? Horn flies with their sharp 5-millimeter-long mouthpart can cause pastured dairy cows to lose 20% of milk production.

Spring is here, which means flies will be coming soon.

To put fly mitigation steps in place, you should identify the type of fly or flies bothering livestock.

The environment that livestock is in can indicate the type of fly pressure that could be present. The two main environments for cattle are barns and pasture.

In barns, the two main flies that bother livestock are house flies and stable flies.

House flies breed in manure piles, animal droppings, decaying silage, spilled feed, bedding and other organic matter.

During the summer, house flies can be spotted on cattle and cause annoyance, but house flies do not bite.

Stable flies, however, do feed on one to two drops of blood several times a day, which can bother livestock and cause performance loss.

Stable flies reproduce in similar scenarios as house flies, and stable flies congregate around the legs and bellies of cattle. Calves are very susceptible to stable flies.

In pasture systems, a few common fly pests are horn flies, face flies, horse flies and deer flies.

Horn flies feast on 20 or more blood meals every day on the shoulders, sides and backs of cattle. On hot or rainy days, horn flies will move to the underside of the belly. Horn flies will reproduce in fresh manure or in manure storages.

Face flies do not bite but can still vector diseases, such as pinkeye and eyeworms. As the name indicates, face flies congregate around the face and eyes of the animal and will reproduce in fresh manure patties.

Horse and deer flies include over 300 species, and they inflict pain and severe annoyance to cattle. These flies will feast on blood, then leave blood pools behind that attract face flies.

Horse and deer flies reproduce in wet areas such as marshes, ponds and streams. Even poorly drained pastures can provide good reproductive grounds.

Pest Management Options

To manage these pests, you should use an integrated pest management plan. Integrated pest management combines cultural, biological and chemical means for fly mitigation.

Cultural forms of pest management would alter the environment that the pest normally thrives in. For example, frequently removing manure and spoiled feed, combined with reducing moisture in barns, can reduce house and stable fly populations.

In a pasture setting, dragging manure patties to allow for manure to dry quickly can help slow the reproduction rate of flies.

If horse and deer flies are an issue, do not graze pastures that are prone to holding water during the wet time of the year.

The biological role in IPM is to have predatory insects kill and consume the flies, eggs and larvae.

A commonly used biological method in barns is to release parasitic wasps weekly or biweekly, depending on the total fly pressure.

Parasitic wasps can be less effective in pasture settings, but other beneficial predators could naturally be present. Dung beetles, for instance, could naturally be present in a pasture.

The last resort should be a chemical method of fly control. Various products can be used, such as ear tags, feed additives, larvicides, baits, rubs, bags, residual premise, whole animal (pour-on), space sprays, and building treatments. In pastures, a chemical method can be most effective for controlling flies. It is important to note that if chemical control is used, all beneficial predators will also be killed.

As summer nears, know that flies will be attracted to manure. Remove manure from cattle loafing areas, or speed up the manure drying process by dragging pastures to help manage flies that may be bothering cattle. Be ready to add a biological or chemical control method if needed. If you are prepared for the fight against flies, you can win.

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May 1, 2021

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Nathan Briggs is a Penn State Extension beef educator from Lancaster County.


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