Know Your Enemy

Horn flies - also fittingly known as Haematobia irritans - are the most pervasive and most costly external parasites of cattle in North America. They're small, black flies, approximately four millimeters long. Adult females lay their eggs in fresh manure, where infestation levels can increase rapidly - up to 4,000 flies per animal in untreated herds. At their peak, horn flies remain on cattle throughout the day and night.

Horn flies pose a unique threat to beef and dairy cattle. Yet, producers often mistake the horn fly for other types of flies, such as the face fly. Unlike horn flies, adult face flies do not bite cattle. Instead, they feed on mucous and watery secretions from the eyes, nostrils and mouths of cattle. Horn flies, on the other hand, can generally be found on the backs of cattle, often clustering on the animals' midlines and spreading down their sides. When at rest, horn flies settle around the base of cattle horns.

Know the Signs

The adult horn fly is a biting insect that takes 20 to 30 blood meals a day. The resulting stress interrupts the grazing patterns of cattle, causing them to go off feed and expend energy in an attempt to dislodge the flies.

According to university research, calves from badly infested herds gain weight more slowly than normal calves and are lighter at weaning by 10 to 25 lbs. If severe infestations are left untreated, cows can go out of condition during the critical breeding period.

Today's Treatment Strategies and Their Major Drawbacks

Current control strategies for horn flies include mechanical, biological and chemical methods. Walk-through flytraps or dragging of pastures to disrupt manure pats can reduce the horn fly population in many environments. Predatory arthropods, such as beetles and mites, can also reduce horn fly populations in some habitats.

In recent years, chemical control has been the most widely used horn fly control strategy. Techniques for application to cattle include rubbing stations, liquid feed, dust bags, sprays, dips, ear tags, pour-on formulations, and oral larvicides in mineral granules, mineral blocks or controlled-release boluses.