Fly and Mosquito Protection

types of repellents | safety | herbal or "homemade" repellents | eradication

Introduction: Repelling bugs from horses is big business. Not only are flying bugs irritating to animal and rider, they often carry disease from one victim to another. For example, the West Nile virus is the latest disease for which an alert has been raised to control the spread of flying insects. When eradication is not likely, repellents are the best course to take to prevent insect-borne disease.

Types of Repellents:
With a few variations and a wide variety of additions, most repellents in use today are based on either the natural or synthetic forms of pyrethrin. Natural pyrethrin is extracted from dried petals of flowers in the Chrysanthemum genus. The most commonly used flower in that family is the African painted daisy which is grown as a crop in several equatorial regions, such as Kenya and India. It not only instantly kills any flying insect it comes in direct contact with, but is an effective repellant because most insects find it extremely irritating.

Like most naturally occurring substances, nature controls the supply line; because humans like to control things themselves, scientists have developed synthetic forms of pyrethrin, called pyrethroids. Mainly, scientists were trying to improve the life of pyrethrin's knock-down power and provide a reliable source of pyrethrin. Although pyrethrin is very effective against most flying insects and is safe for use on mammals, its efficacy is destroyed by the sun. Within an hour or two, the sun can decompose the chemical composition of pyrethrin.

Commonly used pyrethroids, such as cypermethrin, resmethrin, and permethrin, are among hundreds that have been developed in an effort to improve the properties of the naturally occurring substance. Their decomposition time is longer and they come in varying strengths. Some forms of pyrethroids are effective for up to two weeks. The downside is that with increased strength, they are also more capable of being toxic to the creature they are being used to protect. The natural substance, pyrethrin, attacks the neurological system of insects, fish and some fowl. In large enough doses, some of the synthetic pyrethroids are strong enough to attack the neurological system of mammals.

Note: Read all repellant usage labels carefully. Those with stronger pyrethroids have more restrictive instructions for safe usage. Safer products usually must be re-applied more often.

To improve the knockdown life of natural pyrethrin, many manufacturers include PABA sunscreens in their repellant recipes. PABA helps to protect the natural pyrethrin from decomposition. Many manufacturers also include another chemical, piperonyl butoxide (PBO), that works to lengthen the time pyrethrin is toxic to insects. PBO is a popular partner for pyrethrin. It is a derivative of the sassafras tree, with its own capabilities of repelling irritating insects. PBO is also very helpful in combating resistance build-up in insects that occurs with pyrethroids, but not natural pyrethrin. Another popular additive is citronella, a derivative of Cymbopagon nardus, a grass related to lemongrass. It is especially effective in repelling mosquitos.

To buffer the effects of more toxic forms of pyrethroids, repellant manufacturers often add substances such as lanolin or aloe vera to their repellents. Unfortunately, these compounds not only buffer the toxins, they also attract flying insects. When a horse sweats, the repelling compounds often wash off and the attractants are left behind, causing a worse problem than there would have been without the use of a repellant.

Despite being a popular chemical in insect repellents manufactured for the human market, DEET (N, N-diethyl-meta-tiluamide) has not been successful as a horse repellant. In too high of levels, DEET is considered a limited health hazard by the Environmental Protection Agency. It has also been demonstrated that high levels of DEET do not repel any better than lower levels. However, DEET used in too low of levels an actually be an attractant to flying insects.

Drug companies, such as Pfizer and Farnum, all make their own versions of fly sprays. Adam's Fly Repellent (made by Pfizer) comes in both a concentrate and a spray. Both contain permethrin, pyrethrins, piperonyl butoxide, N-Ocytl bicycloheptene dicarboxcimide, Di-n-propyl isocinchomeronate (two insecticides and two repellents) for immediate and residual control of face flies, stable flies, horse flies, deer flies, ticks, mosquitoes, gnats, and house flies. The spray also works on mites, chiggers and lice. In addition, it contains oil of aloe and other emollients to moisturize the horse's skin and produce a shine on the horse's coat.

Both the spray and the concentrate are applied after thoroughly brushing the horse's coat, prior to application, to remove lose dirt and debris. If the horse is washed, its coat should be thoroughly dried before applying the repellent. Avoid any sensitive areas, such as the eyes, nose and mouth, and cover the entire surface of the animal with the spray. Brush the coat against the grain to ensure adequate penetration of the repellent, and allow it to dry before putting on any tack.

Initially, the spray and the concentrate need to be re-applied daily, but may be re-applied every 2-3 days as infestation decreases and protection builds. Re-apply every time the animal is washed.

Farnum's Endure (see page C202) is resistant to sweat and repels horse flies, stable flies, house flies, gnats, face flies, deer flies, mosquitoes, lice and ticks. Pyrethrin, cypermethrin and sunscreen are the active ingredients in it. It should be wiped on with a cloth, and sensitive areas such as the eyes, nose or mouth should be avoided. Furthermore, the person applying Endure should wear protective gloves when applying it to the horse. Endure should not be used on horses intended for human consumption.

Because chemicals with repellant qualities are toxic to bugs, they do have the potential to be toxic at certain levels to other species, such as horses and humans. In areas where heat and humidity are a problem, repellents can cause edema (fluid retention) in horses. Skin irritations and rarely, neurologic problems can also be caused by repellents. In 1994, EPA studies stated that possible "reproductive and developmental toxicities" could develop from use of some synthetic pyrethroids. The study was done on rats and the warning was intended for humans. Furthermore, the rats either inhaled, ingested or were injected with the chemicals.

Systemic toxicity is not expected from dermal (skin) exposure to the chemicals because pyrethroids are processed rapidly by the kidneys and excreted. However, it is important to note that in California, resmethrin must bear a warning label if more than one-thousandth of the amount required to produce a toxic effect is used in a product.

It is wise to test a new formula for allergic reaction in a horse by applying it to a small area of the horse before spraying it all over. As a general rule, to protect the horse's eyes and mouth, spray fly repellent on a soft cloth and wipe it on the head region. Furthermore, apply the repellant in area that it will not over spray onto the horse's food supply. Keep in mind that pyrethrins are toxic to fish. Keep repellents away from water sources.

Herbal or "Homemade" Repellents:
Since man has always looked for ways to improve his situation, there are many traditional remedies for repelling flying insects. Archaeologists attribute finding ancient flower petals in historic Iranian dwellings to pest control. Some other traditional herbal preparations used over the ages have been based on citronella, lavender, eucalyptus, pine needle, tea tree, pennyroyal, wormwood, and apple cider vinegar. (Vinegar is acetic acid. When it is rubbed on a horse's coat, it acts as a repellant if used in high enough concentrations. In low doses, however, it is an attractant.)

"Homemade" fly spray recipes available on the internet are as varied as the sites on which they can be found. In addition to the one or more of the previous ingredients, some recipes include basil, bay leaf, cloves, tansy, cedar, black pepper, rue, rosemary, southernwood, santolina, spearmint, neem, sassafras and/or thyme. They are mixed together with an emollient such as olive oil, and an emulsifier, such as dish washing liquid, then sprayed or rubbed onto the horse's coat.

Again, test the chosen mixture for sensitivity on a small area of the horse. If there is no adverse reaction, apply and see if it works. Usually these herbal remedies work, but do not last as long as the pyrethrin-based recipes. Another compound expected to be available to the public soon is geraniol, a derivative from lemongrass, more potent than citronella, but a member of the same chemical family. It provides double the protection time as pyrethrins do (four hours), and repels ticks and fire ants in addition to mosquitos, no-see-ums, stable flies, and horn flies.


Several products on the market are lethal to flying insects. These products can kill almost any insect that flies (not just biting insects) and therefore, should be used cautiously. Draining swampy areas or standing water near animals is a wise action to protect horses from flying insect invasions. Also, keeping stalls and corrals clean from waste helps to cut down the number of insects that breed near horses.

Following is a checklist of things that can be done to prevent breeding areas for mosquitos and other flying insects: