The battle against flies is constant, but a combination of tactics can keep them at bay. Beyond chemical options, there are also biological methods to add to the mix; and being familiar with the various habits and behaviors of different flies can provide the most effective combination of tactics.

Houseflies and stable flies breed in manure and rotting organic matter such as old hay and bedding. Horn flies breed in cattle manure. Horseflies/deerflies breed in swampy areas and black flies breed in flowing water — often many miles away — so it's impossible to control them at their breeding sites.

Houseflies, stable flies and horn flies can be reduced by a combination of diligent cleanup — not letting manure or old hay/bedding build up to create breeding sites — and use of dung beetles or parasitic wasps. These tiny wasps lay eggs in manure and their larvae feed on fly larvae. Dung beetles break up fresh manure, making poor habitat for fly larvae. Fly control tactics are moving away from dependence on pesticides, due to concern for the environment and pests developing resistance to insecticides.

Importance of sanitation

Manure and wasted hay should be spread thinly for quick drying, or composted. Properly composted material heats sufficiently during fermentation/breakdown to kill fly eggs and larvae. The first line of defense in the battle against flies is to keep them from reproducing — by eliminating breeding sites.

Stable flies (aggressive biters that cause irritation) don't breed in straight cow manure. They prefer decaying matter high in plant waste, such as wet hay or old bedding. In a Texas A&M University study conducted several years ago, researchers found that waste around feeders, make an ideal breeding ground for flies. They estimated the area around one big round feeder produces more than a million stable flies.

In spring before flies emerge, one of the first things to do when weather warms up is to move feeders and spread wasted hay so it will dry, or put it into a big pile to start heating and composting. Otherwise, it may stay wet through summer, providing breeding sites for stable flies.

Predator wasps

The second line of defense is to keep fly larvae from hatching. Parasitic wasps can be purchased from several suppliers. Such wasps can reduce fly larvae by 90% if you diligently reduce fly-breeding sites, put out enough wasps to inhibit what's left, and put out more wasps every 30 days through summer. Even though these wasps are present in the environment, there aren't enough to control the fly population unless you tip the scales by adding more. After all, a female fly lays three times the number of eggs as a female wasp.

These tiny nocturnal wasps spend their lives on or near manure. Adult wasps are harmless because they don't sting or bite. Females search through manure and lay eggs in the pupae of houseflies, stable flies, horn flies and other flies that breed in manure. Wasp eggs hatch quicker than fly eggs and wasp larvae use dormant fly maggots as food.

Parasitic wasps offer the best control in dry climates and dry years. Wasp suppliers recommend releasing them early in the season before flies become numerous. The number of wasps needed depends on the number of animals. A pen with one or two horses or cattle would need 5,000 wasps each month. A larger herd needs 1,000-2,000 wasps/animal/month. Parasitic wasps won't make up for a lack of sanitation, but they can be helpful when used in conjunction with manure/bedding/hay cleanup. Many feedyards try to get rid of wet areas and clean pens once a week when there aren't enough animals in them to adequately trample the manure (some flies breed and hatch in 7-10 days), and use parasitic wasps to help control fly development.

Dung beetles

These insects spend their lives in manure. Adults use liquid components as nourishment and lay eggs in the manure pat. The hatching larvae consume manure. Some species remove and bury balls of manure containing their eggs.

An active population of dung beetles can bury or destroy 95% of horn fly eggs and larvae and about 90% of other cattle parasites that are passed in or depend on manure. Even if the fly eggs hatch in the manure balls, they can't get back up to the ground surface after being buried by the dung beetles.

What's more, birds are attracted to manure containing dung beetles and tear the pats apart to eat them. This helps spread manure and disrupt fly-larvae development. A single manure pat without dung beetles can generate 60-80 adult horn flies.

Fly traps

Biting flies that come in from other areas can be killed before they attack your animals. One effective method is the Epps Biting Fly Trap™, invented by an Oklahoma cattleman and marketed by Horseline Products in Henderson, TN.

Biting flies (horseflies, deerflies, stable flies, black flies, mosquitoes, etc.) are attracted to large, dark objects such as the shape and silhouette of an animal, so the trap is a framework with a large dark portion and some transparent panels. The latter simulate air space above an animal and under its belly, where flies normally would circle before landing to bite and feed.

When flies hit the transparent sheets, they ricochet into trays of water below and drown. A few drops of dishwashing soap added to each tray will break the surface tension of the water so that the insects can't float. They immediately sink and drown.

Research indicates this trap kills about 1 lb./day of biting flies. In fact, a three-year research project at Cornell University, the University of Florida and New York Pest Management compared 15 flytrap products and found this trap's effectiveness was 10 to 1 compared to other methods tried.

The trap catches many flies in the evening when the dark portion is still warm after air cools off; the fly thinks this is an animal. The trap works best in an open area where flies can see it from a distance.

Maintenance requires scooping out dead flies every other day or so with an aquarium net, then adding more water and soap if needed, and changing the water every two weeks. Each tray holds about 3.5 gals. You can also install an electric wire around the trap so animals won't rub on it.

Many ranchers use rotational grazing and want something they can move from pasture to pasture. The new portable model has an aluminum frame (lightweight and easy to move) but is durable and can withstand 90-mph winds. Empty sandbags come with the unit; when filled they sit on the unit's legs and hold it steady in the wind.

Among criteria for participating in a new government conservation stewardship program is that ranchers use environmentally friendly fly control. Such methods include predator wasps, traps for house, stable and biting flies, walk-through traps for horn flies, fly vacuums, bug zappers or ways to enhance populations of species such as martins, swallows, and bats that feed on flies. It must be nonchemical livestock pest control.

For information on the trap, go to www.horselineproducts.com or call 800-208-4846.

For information on predator wasps, go to www.spalding-labs.com.

Heather Smith Thomas is a Salmon, ID, rancher and freelance author of books and articles on livestock management. Look for her titles at amazon.com.