Home - How to Control Horn Flies


The Horn Fly, Haematobia irritans (Linnaeus), was first introduced into the United States more than a century ago. Since then, it has become one of  our most important fly pests of pasture and range cattle. They are small, gray flies, only about 3/16 inch long, about 1/2 to 1/3 the size of the common house fly. Dung beetles will eat Horn Fly eggs and Horn Fly adults are parasitized by certain wasps (Spalangia species and others), and other life stages are fed upon by ants, birds and mice. In spite of these parasites and predators, dense Horn Fly infestations often occur..Horn Flies often congregate on those areas of the body where they are not likely to be disturbed (base of horns, neck, throat, belly, thighs, back, etc.), horn flies suck blood from livestock through their needle-like mouthparts. Such feeding causes weight loss, reduced milk production, and reduced vitality. Furthermore, animals become so annoyed that they may injure themselves while attempting to dislodge the flies. Each fly orientates its head in the same direction as the hair tips of that particular site of the host. Their hosts are primarily cattle but to a lesser extent will feed on horses, sheep, and goats. Both male and female Horn Flies feed on blood by using a slender, black piercing mouthpart that projects forward from underneath their heads. Males feed about 20 times and females about 40 times daily. This feeding activity is painful and annoying to cattle. Horn Flies normally congregate on the backs of cattle, often clustering around the horns and on the midline and spreading down the sides. Sometimes, when the weather is hot, they may move down onto the belly. On finding a host, Horn Flies tend to remain on it and/or others in the same herd for their entire lives, moving to different anatomical sites to regulate their temperature and minimize exposure to the wind. They are strong fliers, on emerging as adults they will fly to find hosts; up to 10 miles has been recorded; but, most probably find cattle within 3 miles. Even though they are strong fliers, most of their adult life is spent on the same host or migrating to new animals in the same herd or flying down to deposit their eggs.. The irritation and blood loss causes cattle to lose 0.3 to 0.5 lbs per day and for dairy animals their incessant feeding clearly causes lower milk production. Large populations of Horn Flies may cause open sores on the head and underline which can predispose their hosts to secondary infections of both disease and parasites. Because of their piercing-sucking mouthparts, Horn Flies are suspected of mechanically transmitting anthrax and other diseases within a herd. Horn Fly numbers of 50 or more per lactating dairy cow or 200 or more horn flies per beef cow are considered to be of economic importance. Extreme numbers of 10,000 to 20,000 flies per animal have been reported and could make blood loss alone (0.5 gal/month) an important factor in reduced production. Horn Fly populations have been generally noted to be lower on dairy cattle than beef cattle. The feed ration fed to dairy animals greatly affects the fly's larvae to be able to survive in the manure. After the flies feed and mate, the female is ready to deposit eggs. She moves to the rear of the cattle host, frequently during early morning. Female flies can lay 14-17 eggs at one time and up to 200 eggs during their lifetime - the eggs are small, reddish-brown and difficult to detect in the manure; and are generally laid in clumps on the fresh manure or on grass and other vegetation covered by the cow pat.  Depending on temperature, the eggs hatch usually within 18 hours, and three instars of maggots/larvae then develop in the dung - often in 14 to 18 days, but in as few as 10 days under ideal conditions. All of the eggs that will hatch are only found in fresh cow manure; the female fly often begins ovipositing before the cow has completed her defecation or at least within ten minutes. Horn Fly maggots are slender and white, narrowing to a point at the head, they live in fresh pats of cow dung and feed on the microbial flora and fauna in it and from decomposition products of microbial action on the dung. When mature, the maggots pupate in or below the pat. Enclosed within the shrunken skin of the last larval instar, the pupa is barrel-shaped and white at first, the outer covering (puparium) soon turns a dark reddish-brown. When the adults emerge from the pupal case, it takes 3 days for the complete maturation of the reproductive organs for egg production. The total life cycle from egg to egg-laying adult usually takes from 10 to 14 days.As summer progresses, more Horn Fly eggs develop but in the more temperate areas, they only mature only to the pupal stage. Rather than emerging as adults, they overwinter (diapause). Diapausing pupae will wait to produce adult Horn Flies the following spring. . When temperatures begin hitting the upper 60's and lower 70's during the day.  Apparently, diapause is triggered by a combination of light and temperature. Because Horn Flies rarely leave their host except to deposit their eggs or to find another host - I believe that safe, organic and very effective control can be achieved by simply spraying, washing or dipping infected hosts once a week for three weeks with Safe Solutions Enzyme Cleaner with Peppermint at a rate of 3 to 4 ounces per gallon of water and/or by simply  feeding the infected cattle hosts - food-grade diatomaceous earth (DE) at a rate of 2% by weight of their dry ration and feeding any infected goat hosts at a rate of 1% in their grain.  


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