So "What About Horse Flies"

Horse flies can be very annoying to cattle, horses and people during the summer months. They are very difficult to control and though it seems they live all summer, there are actually several different species throughout the season.

Only the females "bite," but the blood feeding activities of these large, agile insects can constitute a serious threat to economical cattle performance when populations are large. Horse flies can transmit cattle anaplasmosis and other blood-borne diseases in livestock.

Horse flies are adept at locating warm-blooded animals, including people near swimming pools, streams and in the woods. Apparently the flies are sensitive to parts of the electromagnetic spectrum - their sight may be like "thermal vision" cameras used to detect heat leaks in houses. Most Missouri horse flies have aquatic larval stages. The mother affixes her eggs to vegetation near ponds and streams. The hatching larvae drop into the mud or water where they live as predators for up to several years, depending on the species. When they are ready to pupate, they move from the water to terrestrial sites and generally emerge synchronously; that is, adults of a particular species all emerge at once, which facilitates mate-finding. Horse flies seem to be present all summer long. In fact, synchronous emergences result in one species being present for a time, then being replaced by another species, and so on. To cattle, however, it means being bitten the entire summer. Field trials have demonstrated that daily treatment of cattle with synergized pyrethrins (a natural insecticide extracted from plants of the genus Chrysanthemum) will reduce biting rates by horse flies without adversely affecting cattle. Generally, this has been feasible only for dairy cattle (and for horses) because of their high management level. Few producers are capable of, or willing to, round up beef herds every day, and even if this could be accomplished, the disruption of grazing might actually result in a greater economic loss than that caused by horse flies. Because most horse flies are day-feeders, it is theoretically possible to protect animals and people from attack by staying inside during daylight hours. This is not practical for pastured beef cattle. About 50 years ago, a pair of MU entomologists built a box cattle would walk through that would trigger a pyrethroid spray to be applied (self-spraying.) This allowed animals to treat themselves daily with a small amount of insecticide. Plans are available for the treadle sprayer.

For those who want to reduce horse flies without using an insecticide at all, a horse fly trap was developed by an MU entomologist in the late 1970's. Called the "Manitoba-type" horse fly trap, under Missouri range conditions it was demonstrated to provide measurable control for a few cattle or horses. People have installed these around swimming pools.

Plans and management suggestions can be obtained from the extension office. Our phone number is (636) 583-5141.

Horse flies dish out some big bites and a lot of pain. Most just wait to September and they will disappear.

Ask for MU Guide 7013 Protecting Cattle from Horse Flies · Horse fly trap plans · How to build a treadle sprayer.

Return to the main AgTalk page
		Matt Herring - Agronomy/Natural Resources Ken Bolte - Farm Management/Livestock Franklin County University Extension Center Last revised: 11/28/05		Go to Franklin County University Extension Center page