Managing flies on cattle farms

Stable flies and house flies are considered “premise flies” because they are found in confined areas, such as barns, reproducing in organic debris including bedding and manure. 

Stable flies

• Do they bite cows? Yes, they are blood feeders. 
• What behaviors do they cause in cows? Bunching, foot stomping, tail switching.
• Where are they located on the farm? Found in barns. They reproduce in organic debris, mainly soiled cow and calf bedding.
• Where on the animal are they found? Legs.
• Other notes: Stable fly presence can result in reduced production. 

House flies 

• Do they bite cows? No, they are not blood feeders. They only have sponging mouthparts and they feed on secretions from the nose and eyes. 
• What behaviors do they cause in cows? Minimal avoidance/defensive behavior.
• Where are they located on the farm? They reproduce in organic debris, mainly manure. 
• Where on the animal are they found? Not often on cows, but may spend time around the face.

Other notes: In general, house flies are mostly just a nuisance.

Horn flies and face flies are considered “pasture flies” because they are found on pasture, reproducing in cow dung pats. 

Horn flies 

• Do they bite cows? Yes, they are blood feeders. 
• What behaviors do they cause in cows? Tail switching, head throwing, bunching. 
• Where are they located on the farm? On pasture; they reproduce in dung pats. 
• Where on the animal are they found? Backs, sides, and bellies.
• Other notes: Heavy horn fly infestations can result in substantially reduced weight gain and significant economic losses. Horn flies should be managed when you see around 200 flies per head of cattle.

Face flies 

• Do they bite cows? No, they are not blood feeders. They feed on secretions from the nose, eyes, and wounds. 
• What behaviors do they cause in cows? Ear flapping, head shaking.
• Where are they located on the farm? On pasture; they reproduce in dung pats. 
• Where on the animal are they found?  Faces, especially eyes and nostrils. 
• Other notes: Face flies will actually scrape cows’ eyeballs to get fluid from the surface of the conjunctiva. This feeding can be irritating to cattle and can spread pathogens; in fact, the major economic impact of face flies is the cost associated with the treatment of pink eye. 

To manage stable flies and house flies, start with sanitation. Doing your best to remove possible breeding sites like rotting hay or grain, spilled feed or TMR, manure piles, and other decaying matter is the most effective way to manage stable flies and house flies. A thorough spring cleanout is helpful, followed by frequent debris removal. Scrape, haul, spread, or compost soiled bedding every other week during the summer, if possible. These steps toward cleanliness should be part of any fly management plan, even if you also use additional methods. 

Scouting should also be part of your management strategy. Do this to determine where flies are reproducing on your property. Start scouting by examining areas that contain organic matter - bedding, feed, manure piles - and more. You should begin looking for signs of flies in the spring. Dig or scrape around in areas with organic matter and search for larvae (maggots) and pupae to figure out where your trouble areas are. It is ideal if you can clean out these problem areas in the spring, which can help decrease fly breeding over the next few months.

Sticky traps can help monitor fly populations to help you determine when you might consider additional management practices like chemical control. 

Fly baits can be useful when used in conjunction with other management techniques but are generally most effective in attracting house flies. 

Fly traps like the Spalding Cow-Vac or the Bruce Fly Trap (which you can build yourself) can effectively reduce the number of pasture flies, particularly horn fles, found on cattle.

Brand names are mentioned as examples only. The University of Minnesota does not endorse these products.

Premise Flies

Premise sprays can help with stable flies and house flies, but should be paired with sanitation efforts. Ear tags, back rubbers, dusters, and pour-on insecticides are not considered to be effective control methods for premise flies. 

Pasture Flies 

Ear tags are effective in managing face flies. Dust bags and back rubbers can also be effective if they are placed low enough to contact the animal’s face. If you use ear tags, be sure to rotate the active ingredient of your tags (use different insecticide classes) to help minimize resistance issues.

Horn flies should be managed when you see around 200 flies per head of cattle. Options for horn fly management include: pour-ons, sprays, dust bags, feed additives, and insecticide ear tags. Feed additive products contain insecticides that pass through the animal’s digestive system and kill horn fly larvae in the manure. These products are effective at reducing the number of larvae, but that does not necessarily reduce the number of adult flies because adult flies are mobile and can easily move to and from neighboring herds.

Biological management of flies means using other organisms to manage fly populations. Some animals, even some other insects, are considered natural enemies of flies because they either feed on flies or their larvae (maggots) or parasitize them. Research is not conclusive as to whether predators or parasitoids significantly suppress fly populations.

Predators 

Birds, such as chickens, may eat fly larvae. Chickens around the farm yard may provide some amount of help with fly management. Chickens could also potentially fit in some pasture grazing systems, following cattle to prey on larvae in dung pats. Research is not conclusive that this causes significant decreases in fly populations.

There are also some predatory beetles, such as rove beetles and hister beetles, that eat fly larvae in dung pats on pasture. However, many insecticides that kill fly larvae have the potential to kill predatory insects, too. If you are hoping to use other insects to help manage your fly populations, you will want to choose a more selective insecticide, carefully select the areas in which you use insecticides, or forego insecticides to protect your beneficial insect populations. 

Parasitoids

There are species of parasitoid wasps that lay their eggs inside fly pupae. This ends up killing pupae and prevents adult flies from emerging. You can attempt to attract these beneficial, parasitoid wasps to your farm naturally by providing biodiverse habitat. Some companies also sell these wasps, often named something like “fly parasites,” “fly predators,” or “dairy fly parasites.” Generally, these wasps are most effective in confined areas. 

Parasitoid wasps can provide effective management when used with other methods, especially diligent sanitation. However, insecticides will kill the wasps, so insecticide residuals should be avoided in areas where you might release the wasps if you are using parasitoid wasps as part of your management strategy.