Guide to Fly Control for Horses

It's Easier Than You Think To Win THe Battle Against Flies!

There are over one million known species of insects in the world. Thankfully only a tiny percentage of insects are an issue for people with horses and other animals. This guide focuses exclusively on flies as they are the worst problem insects for most animal owners.

By gaining some basic understanding of fly biology, particularly what encourages and discourages their reproduction, you can reduce their numbers to tolerable levels, with no or only a minimum use of insecticides. On the following pages are ways and means of identifying, preventing and controlling these insects in and around your stable, farm, home and yard using an integrated pest management approach.

Often the simple release of Fly Predators, plus modest improvements in manure management and perhaps a few fly traps is all that will be needed. More comprehensive approaches, including initial careful and selective use of insecticides, may be necessary for the fastest control if the pest fly problem has been allowed to become severe. This is because most of the 'natural' controls prevent future flies, but do not affect existing adults. Since adult flies live approximately 21 days, you will either need to put up with them for that long or use traps and baits or careful pesticide application to reduce their population rapidly.

The first step is to identify the insect(s) that are plaguing you and your animals. Most of the common pest flies are easy to identify simply by comparing one with the illustrations on the following pages. When the fly is identified, then use the methods listed that focus on the prevention and control of that species. This is important as the variety of flies that bother you can come from dramatically different sources. For example, not all the flies that are attracted to a horse's face are 'face' flies. Most are probably House Flies and the smaller Lesser House Fly which are controlled somewhat differently than Face Flies.

The House Fly and the Stable Fly are the primary pest fly species that create problems as well as being the most widely distributed.

Fortunately both of these can be very effectively controlled by good sanitation and Fly Predators. If sanitation is immaculate then fewer or no Fly Predators may be needed. Conversely, if “immaculate” is beyond practical then adding a few more Fly Predators and perhaps some traps will still yield very satisfactory results.

Note, all other insects listed other than Horn and possibly Cluster Flies are not suitable hosts for Fly Predators and therefore Fly Predators will not help in their control.

Using a preventive solution like Fly Predators or making the area less “fly friendly” requires that you treat the locations where the pest flies are reproducing. In almost all cases this is NOT where you see the adults flies that are bothering you or your animals. Often you will see the most flies in the barn but its highly likely that only a small percentage of those flies came from the barn. Instead they most likely came from the pasture, corrals, the manure pile, the neighbors animals, etc. If you’ve only been spraying, using traps, baits or sticky tapes in the past you have to think differently when using biocontrol.

Why Fly Control is Important

Flies are a major cause of discomfort and warm-weather diseases of horses. Flies are found everywhere horses, cows, dogs and other animals are concentrated and cause many problems. Some flies torture horses and your other animals by biting. Many horses develop allergic skin conditions from being bitten, and fly bite allergy is the most common skin disease found in horses. Stomping at flies and kicking at them causes shoe boils on the elbow, belly sores and abscesses. Dogs are also sensitive to fly bites on their ears.

Non biting flies irritate horses' and cows' eyes, often causing serious infections. They are attracted to wounds, complicating them with infections and often causing persistent and dangerous 'summer sores' on horses. These insect pests also carry contagious disease from one animal to another. For example, if a fly is attracted to the nasal discharge of a horse with a cold, flu, VS or strangels, it easily transmits the infection to the next horse it lands on. A similar disease transmission path occurs with Pink Eye in cattle.

Basic Fly Biology

Its been said that every creature has it's purpose. For flies their purpose is to decompose rotting organic matter such as manure, dead plants and animals. If you have an abundance of material needing decomposition, you get an abundance of flies.

Flies have four stages in their life cycle (shown in the diagram above). Adult house flies lay eggs on or close to a larval food source of rotting organic matter (i.e., manure but also compost piles, rotting hay, etc.) the eggs hatch within hours into larvae (maggots). The larvae feed and then in no less than 5 days they pupate forming a cocoon. Inside this cocoon they metamorphosis into an adult fly which takes at least 3 days. This is the same process a caterpillar goes through as it turns into a butterfly. You can use these minimum transformation days to your advantage.

The pupa is light to dark brown and looks very much like a dark grain of rice or a rodent dropping. This is the stage the Fly Predator takes over killing that immature fly. The pupa is also the stage that flies “hibernate” when the temperature drops below 47oF allowing them to make it through the winter. Note there are no “baby” flies, when they emerge from the pupa, they are full size. The smaller flies you see are just different species. For example the House Fly has a smaller cousin, the Lesser House Fly.