Springtime and recent rains seem to have brought about the horn fly on cattle in our area. The name be misleading as they congregate on cattle without horns. Introduced to the U.S. from Europe in the late 1800s, they were named “horn fly” because they clustered at the base of the horns on cattle. Cattlemen know the flies now congregate almost everywhere on the cow’s body.
Horn flies are the same color as a house fly but much smaller – about 3/16 of an inch in length. They lay their eggs in a freshly dropped cow manure pad where they hatch in about 24 hours. The manure needs to be less than an hour old because the female fly must deposit eggs inside the manure before the surface hardens.
The eggs will then hatch into larvae (also known as maggots) and after four to five days will pupate for a week to 10 days and then eventually emerge from the pad. Within two-three hours after emerging, they can be feeding on cattle, where they can take 30-40 meals per day.
The females can mate within two days after emerging and lay several hundred eggs a day later and for several days afterward. The entire life cycle takes 12-14 days in the summer. Horn flies appear on the first warm days of spring and are active until the fall and cool weather. They prefer warm, humid days.
Horn flies are quite the irritant for cattle as they puncture the skin to suck blood and usually are found on parts of the cow’s body not easily reached by the head or tail. Horn fly bites can cause extensive hide damage.
When temperatures are high, they move to the shaded parts of the belly. Unlike most flies, they remain on the animal day and night. Large numbers of horn flies cause constant irritation and can cause weight loss, loss of condition, and lowered milk production.
They can also transmit several diseases including Stephanofilariasis, a condition caused by a small parasite. This parasite causes the cattle to scratch and scrape themselves until they bleed to relieve the pain. Damage is so severe that it causes the large scars on the navels of many commercial cows.
There are many management practices and several products and subsequent methods of application to help control horn flies. Management practices include pasture rotation that helps break the life cycle and dragging small pastures and traps to break up manure pads.
There are biological control methods including mites, beetles and wasps that feed on the larvae as well as dung beetles, which help break up manure pads. Interestingly, the much-hated fire ant even helps to reduce the numbers of horn flies in the pasture as they consume the fly maggots.
Apart from waiting for natural control, stockmen have several options they can purchase to protect their cattle. Direct pest control methods include a variety of chemicals that are either self-treatment or applied as sprays, pour-ons, dips, ear tags, dust, back rubs, insecticide balls and in dust bags. Insect growth regulators (IGRs) in mineral or other feeds inhibit the larvae’s development into adult flies. Each product and application have pluses and minuses, but a combination of management and chemical control yields the best results if not complete control. Many savvy cattlemen use a combination of approaches that may include pasture rotation, ear tags, as well as an IGR.
For more detailed information on the active ingredients and methods of control, there is an AgriLife Extension fact sheet entitled “Protecting Cattle from Horn Flies” written by Dr. Sonja Swigert, an Extension Veterinary Entomologist with the Texas A&M AgriLife Extension Service. She has another publication that discusses other external parasites and their control. That one is called “Managing External Parasites of Cattle”. If you cannot find it online, feel free to contact your local AgriLife Extension office.
