Vet's Corner

Vet's Corner

A Natural Method of Fly Control
  • By Robert M. Miller, D.V.M
  • Reprinted from Western Horseman

Flies are a major cause of discomfort and warm-weather diseases of horses. House flies, biting stable flies, horn flies, and face flies are found everywhere horses are found, and cause many problems. Flies torture horses by biting. Many horses develop allergic skin conditions from being bitten, and fly bite allergy is the most common skin disease found in horses. Stamping at flies and kicking at them causes shoe boils on the elbow, belly sores, and abscesses. Flies irritate horses’ eyes, often causing serious infections. They are attracted to wounds, complicating them with infections and often causing persistent and dangerous “summer sores” (habronemiasis). These insect pests also carry contagious disease from one horse to another. For example, if a fly is attracted to the nasal discharge of a horse with a cold, flu, or strangels, it easily transmits the infection to the next horse it lands on.

In short, flies are PESTS. Horsemen have always known this, and for centuries have tried to minimize the problem by hauling away manure (where flies breed) and protecting their horses with repellents (such as oil of citronella), face masks, protective blankets and boots, and the use of fly netting and screens.

During World War II, DDT was used extensively to control malaria-bearing mosquitoes and typhus-causing lice. The introduction of chemical insecticides was hailed as one of technology’s greatest advances. Indeed, these chemicals had a profound effect upon controlling insect-borne diseases of man and animals, and enormously increased agricultural production by controlling insect pests.

When Rachel Carson wrote her book Silent Spring, warning of the danger that indiscriminate pesticide use could create, she was widely criticized as an alarmist; but within the past two decades, the world has become increasingly aware that chemical insecticides are not a cure-all, and that their use has created problems as serious as the pests they were designed to control. These problems include the development of insecticide resistant pests, contamination of human and animal water and food supplies, and damaging side effects in both animals and man.

It has long been known that there are many insects that are beneficial and, in fact, vital to man. Some of these “friendly” insects can be used to control “pest” insects. For example, ladybugs and lacewings help control agricultural pests.

Similarly, a tiny insect called the Fly Predator can help control those flies which create such a nuisance around the stable. Fly Predators are very small members of the wasp family, but they do not sting or cause people any problems. They are nature’s method of controlling pest fly populations. They attack the immature forms of pest flies where they breed, particularly in manure. And they are specific to flies, never attacking anything else.

In 1980 I was at a show-horse stable treating several horses. It was just before noon, and the temperature was about 100 degrees Fahrenheit. I suddenly realized that there were no flies about causing their usual annoyance. “What are you using to control flies?” I asked, wondering if they had found some new potent insecticide. “Fly Predators” the stable manager replied.

I had heard of this biological method of fly control, but had not seen its effectiveness before. That summer I found that several more of my clients were subscribing to a Fly Predator service, with results ranging from good to excellent. At my own ranch, the fly problem was very bad that year, despite the daily use of repellents on the horses, and the use of sprays around the barns. Two big fly traps hung beneath the barn eaves, and I had to dump them twice that summer because they had filled with dead flies.

The first summer I started using Fly Predators, supplied by Spalding Laboratories of Arroyo Grande, California, I started early in the spring, before the fly problem got bad. I followed Spalding’s instructions, using my monthly shipments of flies exactly as they told me to in the corrals, around the barn, on the manure pile, and in the pastures. I was very pleased with the results. My fly problem was greatly reduced. If my neighbors had been on the same program, the results might have been even more spectacular. One fly trap accumulated only about two inches of flies all summer and the other even less. I continued using fly repellants on the horses several times a week, but I used no other traps or baits (even though the company suggests that they be used in conjunction with the predators) because I wanted to objectively evaluate the effectiveness of the program.

The cost of such a program is nominal. It compares to what the stable owner will spend on conventional methods, but in my opinion, the results are superior. You are preventing flies instead of killing them after they hatch. The flies will not develop chemical resistance. Most important, the environment is not becoming contaminated, because a natural biological control method is being used.

Before one adopts a Fly Predator program, several things must be understood:

  1. The program should be started early and conducted according to the instructions.
  2. Don’t expect 100 percent results. Nothing now known can give 100 percent fly control. The predators minimize the fly problem. They don’t eliminate it.
  3. Do not combine a predator program with indiscriminate pesticide spraying with insecticides. The chemicals will kill the Fly Predator, thus ruining the program. However, the use of repellents on the horses, the use of traps and baits, and the use of selective area spraying is encouraged.