Alternative Methods of Horn Fly Control

By: Heather Smith Thomas

Of all biting flies, horn flies cause the most problem for cattle because adult flies spend almost all their time on the host. During fly season, an animal may have thousands covering neck, shoulders and back, with smaller numbers on the rest of the body or along the midline of the belly. Studies have shown that a calf with more than 200 flies during summer may weigh 15 to 50 pounds less at weaning than calves with fewer flies.

Horn flies have a short life cycle—from egg to adult in 10 to 20 days. Adults live about three weeks and suck blood so they can produce eggs—which they lay in fresh manure. 

For several decades the most common way to control horn flies was with pesticides such as pour-ons, rubbers and dusters (self-applicators) and insecticide ear tags. Horn flies develop resistance to these chemicals after a few generations, however, and chemicals must be rotated yearly or every other year. Another drawback is that there have been some indications that certain pyrethroids may have negative effects on semen quality of bulls. Many stockmen are now trying to use fewer chemical pesticides to control parasites.  

One alternative for horn fly control is to use natural methods such as parasitic wasps (that work best in small areas like a feedyard or barnyard) and dung beetles. The tiny wasps can be purchased in immature form from several insectaries around the U.S. The adult wasps lay their eggs in fly larva in manure and the young wasps eat the fly larvae.

Dung beetles live in manure. The adults feed on liquid portions, and lay eggs in manure. The hatching larvae consume more manure. Dung beetles help control all parasites that depend on manure for part of their life cycle. Some species of beetles bury manure, which helps fertilize the soil.

 There are more than 90 species of dung beetles in North America, including some imported from Africa during the 1970’s and 1980’s. The beetles bury 95% of horn fly eggs and larvae and 90% of internal parasites passed in manure. 

Some types of dewormers and pesticides destroy dung beetles, however, killing at their larval stage. Use of ivermectin products can decimate beetle populations because fresh manure of treated cattle is toxic to beetle larvae. However, some products do not have an impact on dung beetle larvae.

Some stockmen with small herds control flies with Muscovy ducks. This breed is not a water duck; it eats insects. The ducks can range freely in pens and pastures and are prolific breeders. They follow cattle around, searching through manure for fly larvae and scattering the piles. It takes about four ducks per cow to adequately control the fly population. The ducks also eat adult flies and pick flies off cattle when they are lying down.

Other ways to reduce flies without chemicals

Some farmers use apple cider vinegar during summer in the cows’ water supply to repel flies. This makes the skin slightly more acidic (changes the pH) and flies are less attracted, reducing fly load on the animals.

Some rotation grazing programs minimize horn fly development, if the cattle are moved often enough, and far enough, to new pastures to get away from the manure where flies are breeding. If cattle are moved far enough, and don’t come back to that pasture for several weeks, this can help break the life cycle. Moving cows every day or every few days can make a big difference. If they are not moved far enough away, however, the flies can still find the cows.  

Walk Thru Horn Fly Trap

First constructed by USDA entomologist Willis Bruce before World War II, this fly trap gained new interest in the late 1980’s after horn fly resistance to insecticides became an issue. Detailed instructions for building a simple walk-through trap are available from University of Missouri Extension. 

Cattle enter the 10-foot trap through either end — like going and coming from water or along a travel route from pen to pen. As they walk through, they contact a series of canvas or carpet strips that dislodge most of the horn flies on their backs and sides. The dislodged flies are attracted to light and travel toward the screened sides of the trap, and cannot escape. Zigzag screening forces them to crawl from a large opening through a smaller one. As they go through this cone effect, they are trapped between the exterior screen on one side and the zigzag screen on the other. 

A combination of several strategies (fly trap, dung beetles, etc.) can reduce horn flies to less damaging levels.