This week I thought I would share some information about horn flies and their impact on cattle. Economically, the horn fly is the most important arthropod pest of pastured cattle in the United States. Losses in the U.S. have been estimated at about $800 million annually.

These losses are greatest to lactating cows and growing claves. Studies have shown that effective horn fly management can result in a 15-30 pound increase in weight in stocker calves during the growing season.

University of Arkansas researchers noted a 17 pound reduction in calf weaning weights for every 100 flies feeding on the cow. Horn flies have long been implicated in the spread of summer mastitis in non-lactating mammary glands. The horn fly can also serve as an intermediate host of a nematode that causes skin inflammation along the belly of cattle.

The horn fly was accidentally introduced into the U.S. from southern France prior to 1886. It is known for spending most of its time on the back and shoulders of animals. During very hot or rainy weather, horn flies can move to the belly of the animals making a count more difficult. Horn flies only leave the animal to lay eggs on fresh cattle manure, less than 10 minutes old. Both sexes of flies feed on cattle by taking 20 to 40 blood meals per day.

Populations of up to 10,000 flies per animal have been documented. Development from egg to adult occurs in as little as 9-12 days. Horn flies survive the winter as pupae in the soil. Adults emerge in mid-March with populations peaking in late May or early June.

Horn fly presence or absence is temperature dependent, while abundance is influenced by humidity and precipitation. During the dry and hot months of summer, populations will normally decrease, but in September, as temperature decreases humidity and rainfall increases, the populations will peak again.

Monitoring horn fly abundance on cattle is important in making appropriate management decisions. It will also provide early warning to potential insecticide tolerance or other issues that negatively impact control. Horn fly abundance should be monitored weekly throughout the fly season. Monitoring is best achieved by counting the number of horn flies on the head, shoulders and back of at least 10 cattle. When average counts approach the economic threshold 150-200 flies per head for beef cattle and 75-100 flies per head for dairy cattle control or supplemental control should be considered.

For more information on horn flies or fly control please contact The Newton County Extension Office at 870-446-2240. Remember to check out our Facebook UAEX Newton County Extension Agriculture News. As always The University of Arkansas Division of Agriculture is an equal opportunity/equal access/affirmative action institution.

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