Large populations of horse flies and other biting flies feeding on dairy cattle reduce milk flow and greatly irritate animals while they are grazing. Horse flies, deer flies and mosquitoes have also been implicated in the mechanical transmission of bovine anaplasmosis. The larvae of horse flies and deer flies both develop in aquatic or semi-aquatic situations. This stage lasts from one to three years. Control of horse flies and deer flies is very difficult.
Insecticides are usually ineffective since the insects spend little time on the animals.
Insecticide treatment of breeding areas is also impractical. Fortunately, these flies are only present a short time and in small numbers in most areas of Kentucky. Technically, cattle grub infestations are a form of myiasis. House flies and blow flies will sometimes lay their eggs in the manure-matted coats of young calves that have bad cases of the scours. When cattle are maintained in pens without adequate dry bedding their hair coats can become matted with manure and they are also susceptible to infestations by these flies.