by: Heather Thomas

The battle against flies is constant, but there are ways to reduce these costly and irritating pests—without toxic chemicals. There are several types of pest flies, with different habits and behavior, so a combination of tactics is usually most effective when trying to eliminate or reduce flies. House flies and stable flies (the latter are aggressive biters, tormenting horses and cattle) breed in manure and rotting organic matter such as old hay and bedding. Horse flies and deer flies breed in swampy areas and black flies breed in flowing water. These biting flies may come to your place from many miles away and it's often impossible to control them at their breeding sites.

Houseflies and stable flies on your farm can generally be reduced by a combination of diligent clean-up—not letting manure and old hay/bedding build up to create breeding sites--and use of parasitic wasps. These tiny wasps lay their eggs in the manure and their larvae feed on the fly larvae.

Manure and wasted hay should be removed daily from stalls and pens. It can be spread thinly for quick drying, or composted in a covered pile. Properly composted organic material gets hot enough during the fermentation/breakdown process to kill fly eggs and larvae. The first line of defense in the battle against flies is to try to keep them from reproducing, and the best way to do that is to eliminate breeding sites.

Stable flies don't breed in straight cow manure, but will breed in horse manure. They actually prefer any kind of decaying matter that's high in plant waste, such as wet hay or old bedding. Texas A&M University did a study several years ago and found that if people don't clean up the areas where they feed big bales in feeders this makes ideal breeding ground for flies. The researches estimated that the area around one big round feeder would produce more than a million stable flies.

In the spring, before flies emerge, one of the first things to do when weather starts warming up is to move the feeders and spread the wasted hay around so it will dry out. Or it can be put into a big pile so it will start heating and composting. Otherwise, this material will stay wet through the summer and continually provide breeding sites for stable flies.

The second line of defense is to try to keep fly larvae from hatching. This is where parasitic wasps can be beneficial. They can be purchased from several different suppliers, including Spalding Laboratories. These wasps can help reduce fly larvae by about 90 percent if you diligently reduce fly breeding sites and then put out enough wasps to inhabit what's left. You also have to keep putting out more wasps every 30 days through the summer. Even though these wasps are generally present in the environment—wherever there are flies—there are not enough of them to control the fly population unless you tip the scales in your favor by putting out more wasps. A female fly lays three times the number of eggs laid by a wasp.

The wasps work best for fly control if there are just a few breeding sites and you can put out enough wasps to deal with the fly maggots. These tiny nocturnal wasps are almost too small to see, and spend their entire lives on or near manure. Adult wasps are harmless to humans or animals because they do not sting or bite; they simply lay their eggs in manure. The females search through the manure and lay eggs in the pupae of houseflies, stable flies, and any other flies that breed in manure. The wasp eggs hatch quicker than the fly eggs and the wasp larva use the dormant fly maggots as food, killing the fly before it can fully develop.

Parasitic wasps give more control in dry climates and dry years. If you have a wet season—which gives more ideal habitat for breeding flies—you may not have enough wasps or enough dispersal of the wasps to deal with the fly population. The number of wasps needed is generally based on the number of animals you have. Wasp suppliers recommend releasing them early in the fly season before flies become numerous, and putting out more wasps every 30 days through fly season, spreading them around in corrals and barns where there's manure. A paddock with one or two horses or cows would need 5,000 wasps each month, whereas a facility with three to five horses or cows would need 10,000 wasps per month, and a larger herd should have about 1000 to 2000 wasps per animal per month. Parasitic wasps will not make up for lack of sanitation, but used in conjunction with manure/bedding/hay cleanup, they can be helpful.

Environment-Friendly Fly Trap

The biting flies that come onto your place from other areas can only be addressed by trying to kill or trap them before they attack your animals. One effective method is the Epps Biting Fly Trap™, invented by a cattleman in Oklahoma. It is now made and marketed by Mark and Virginia Bonacquista (Horseline Products) in Henderson, Tenn.

Alan Epps had about 250 cattle, and they were constantly tormented by horse flies—they were miserable and bloody, and covered with welts from the bites. He'd tried everything on the market to control the flies, but nothing worked very well.

For three years Epps experimented with different things and researched the habits of biting flies. Flies are attracted to the shape and silhouette of an animal, so Epps made a framework of wood with a large contrasting surface area—a dark portion and some transparent panels. The latter simulate the air space above an animal and under its belly—areas where flies normally circle before landing to bite and feed. When the flies hit the transparent sheets they ricochet into trays of water below them, and drown.

By 1998 Epps had developed a workable unit and presented the idea to Farnam, who manufactured it until 2007. “At that point Farnam was bought out by Central Life Science and that company closed the farm division. Every product in the farm division was discontinued—waterers, gates, etc. and the fly trap,” says Bonacquista.

“We'd been using their fly trap on our farm for five years with great success, and called the company to order more clear plastic sheets, which need to be replaced every few years--the only things we'd ever had to replace on the traps. We loved those traps; we'd found out about them through our veterinarian. We'd been frustrated after using all the sprays, fly collars, rub-ons and feed throughs. Nothing seemed to work against horse flies, especially for two of our mares. They were running through thickets and brush, cutting themselves up trying to get the flies off,” he says.

“When I called to order more sheets and found they were no longer available, I contacted Mr. Epps directly and signed a contract with him to manufacture the trap ourselves and distribute it,” says Bonacquista.

Farnam's entomologists claimed the trap would attract and kill flies in a 40-acre area. “I didn't want to make such a bold statement, but we can guarantee it will clear the biting flies from 20 acres,” he says. This does not include houseflies, just biting flies.

All biting flies (horse flies, deer flies, stable flies, black flies, mosquitoes, etc.) are attracted to large dark objects. “If you have a black horse and a light horse, or a black cow and a light colored cow, flies are more attracted to the dark one. They also tend to fly around the animal two or three times before they attack. The two plastic sheets are on a 45-degree angle with the trap. That's the only place there's light,” he explains. The flies run into these sheets, thinking they are flying over the animal or around its legs.

They hit the clear plastic sheets, fall into the water trays, and drown. “You add eight drops of dishwashing soap to each tray. The soap breaks the surface tension of the water so the insects can't float,” says Bonacquista. They are immediately wetted completely, and sink and drown quicker -- unable to float, swim or climb out.

“Within less than a month of using the trap, we'd reduced our fly problem. Research showed that this type of trap kills, on average, about one pound of biting flies every day,” he says. Actual amount will depend on the fly population in your area.

“Each year, our fly population is less. Now we're only getting a pound of flies every week. When you start killing off half a million biting flies, it makes a dent in the population because they can't reproduce that quickly.”

He refers to a three-year research project at Cornell University, University of Florida and New York Pest Management. “The researchers told me our trap's effectiveness was 10 to 1 compared to any other method they tried, looking at 15 other products. They also tested our trap for three years in upstate New York on dairy farms, looking at a non-chemical approach versus use of pesticides.” The problem with pesticides is that they only work short term and some insects develop resistance. Another drawback is that many chemicals are toxic to other forms of life as well.

Fly predator wasps help control houseflies and stable flies that lay eggs in manure and old hay or bedding, but have no effect on horse flies and deer flies. The fly trap will kill any of the biting flies.

The trap is simple. “Alan Epps looked at the natural behavior of these flies and created this trap to trick them. It's black, produces a silhouette and gives off heat. It catches a lot of flies in the evening when the dark portion is still warm.” When air cools off, the black trap is warmer, and the fly thinks this is an animal. The fly can still see the light part, so that's where it flies. If you stand nearby you can hear flies hitting the sheets—ping, ping, ping—and falling into the water traps.

The trap costs $295. “This is a one-time investment. I've talked with people who've had their traps since 1999 and they still work well. You just need to replace the clear plastic sheets because they deteriorate, but those only cost $8,” he says. This is inexpensive, compared with what you'd spend for sprays, repellents and wipe-on products for horses, or for chemicals to treat cattle. Customers in regions with a long fly season may need to replace the sheets every year; in other areas the sheets might last for three years. Bonacquista replaces his every two years.

The traps work best when placed in an open area where flies see it from a distance. When set up, the trap is about five feet tall and seven feet long. All you have to do is scoop out the dead flies every other day or so with an aquarium net, add more water and soap if needed, and change the water every two weeks. Each tray holds about 3.5 gallons of water. There's no messy bait to handle, and it doesn't matter what kind of dish soap you use. If the trap is in a pasture, you can put an electric wire around it so animals won't rub on it or damage it.

Last year Bonacquista started marketing a portable trap as well. Many ranchers are now using rotational grazing and want something they could move from pasture to pasture. The portable model has an aluminum frame (lightweight and easy to move) but is very durable, able to withstand 90 mph wind.

“We include four empty sandbags with that unit, to hold it steady in the wind. Most people just use two. When you move the trap you just pick up the sandbags and put them on your trailer or the back of a pickup when you move the trap from pasture to pasture. Sandbags will hold it down in a 90 mph wind. We tried stakes, but the wind can pull them out. The sandbags are green and match the environment, and sit on the legs of the unit,” he says. Some of his customers move their cattle frequently -- in an intensive grazing system -- and move the trap each time they move cattle to the next pasture.

Bonaquista says the government recently started a new conservation stewardship program for farmers and ranchers. “Part of the criteria is that you use environmentally friendly fly control, with specifications about what you can or can't use. You have to incorporate things like fly predator wasps, traps for house and stable flies, traps for biting flies, walk-through traps for horn flies, fly vacuums, bug zappers--or use ways to enhance populations of martins, swallows, bats, etc. that eat flies. It has to be non-chemical livestock pest control. Our product fits nicely, because soap is not harmful to the environment.” Some organic dairy farmers use a soap product made by Amway, called LOC (liquid organic concentrate), which is safe enough to drink. They put this in their flytraps and it works just as well as any other liquid soap. Common dishwashing soap is also fine, however.

For more information on the traps, check the website: or call 800-208-4846.

For information on predator wasps, check


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