It’s that time of year when flies return to our barns and become a nuisance for farm workers and animals alike. During an Iowa State University Extension webinar, Phillip Jardon discussed how the four main types of flies seen on dairies reproduce and where they live, noting that when we understand their life cycle, we can form more effective control strategies.

Stable flies are the most painful to cattle, the dairy extension veterinarian said. This is because they feed solely on blood and have a sharp, piercing mouth to bite animals. Stable flies move close to the ground, so you will generally see them on animals’ legs and maybe the belly, always facing upward. They will only eat for a few minutes a day and then rest somewhere else, so only a small number of the stable flies present in an area will be visible on an animal at any point.

“It doesn’t take very many flies to be of economic importance,” Jardon said of these parasites.

If you need to treat animals for stable flies, be sure to spray the legs, he emphasized. Pour-ons over the back won’t reach where these insects affect cattle. But more important is to destroy the breeding area, Jardon said. Stable flies reproduce in decaying organic material like used bedding, buildup at a feedbunk, or rotting hay. He encouraged cleaning up these piles to limit stable fly proliferation.

The other parasitic fly that feeds on blood is the horn fly. Jardon said these are more of a concern in beef cattle than dairy cattle but can be a problem if dairy animals are on pasture. Horn flies are considered a “pasture fly” because they reproduce in fresh manure, he explained. Adults will then spend nearly all of their time on the animal. They are small flies that will face down and typically be found on the shoulders and back. They may all fly off in a fog when disturbed.

Jardon noted that horn flies can seriously impact animal growth and performance. There may be 8,000 flies on an animal at one time, and with each one biting 20 to 40 times a day, an animal can lose more than 2 liters of blood in one day. These flies are often also the culprit behind so-called summer mastitis that may affect heifers entering the milking herd.

Tags, sprays, and oilers can all be effective to control these flies, he said. He also encouraged feeding an insect growth regulator to control the number of horn fly larva in the manure. This needs to be added to the diet before flies appear, Jardon specified.

Pastures and fresh manure are also prime breeding ground for face flies that can spread pinkeye and other diseases. These flies do not bite or drink blood but will redigest food they throw up. They congregate around the animals’ eyes and will drink tears and mucus.

Jardon said that ear tags, sprays, and oilers can also control face flies. Again, anything that will disturb manure piles will be most effective at preventing flies from developing to begin with.

Finally, the house fly is the other “sponge feeder” that does not bite but can be a nuisance on farms because they prefer to be around other living things. Like face flies, they can carry many pathogens, and like stable flies, they reproduce in decomposing waste or dirt.

Destroying those breeding areas is the best strategy for limiting house flies. Jardon also said they are the only fly that can be controlled with baited traps. Spraying or treating animals will not be helpful, he noted.

Identifying the types of flies buzzing around your farm can help in developing targeted strategies that disrupt their life cycle, which is typically only one to three weeks. “We spend too much time concentrating on killing the adults,” Jardon said in summary. Preventing flies from reproducing will save time and trouble in the long run.

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(c) Hoard's Dairyman Intel 2024
May 6, 2024
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