by Marilyn Munzert
There’s a current trend in society toward more natural products and remedies, and insect repellents for horses are no exception. But are natural products effective, and are they really safer? Examining the ingredients in repellents and understanding how they work can enable you to choose the insect repellent that’s best for you and your horses.
Natural repellents are generally thought to contain herbal ingredients that are safe, while chemical repellents are perceived to contain man-made ingredients that are more dangerous. The distinction is not always clear-cut.
Although chemical repellents contain synthetic active ingredients, and the active ingredients in natural repellents are herbal in origin, many natural oils are derived from plants using chemical processes and, therefore, could be called chemicals.
Secondly, natural does necessarily mean safe. Many common natural substances, such as aloe and citronella for example, can cause allergic reactions in some horses and people.
Most insect repellents that contain poisons “repel” flies mainly by killing them. In order for these products to work, the insects have to land on the sprayed horse and touch or ingest the poison. So, just because flies land on a horse right after he’s been sprayed doesn’t mean this type of repellent isn’t doing its job.
Caution: Insecticides in fly spray are non-selective and will kill beneficial insects, like fly predators, as well as pests.
Another thing to be aware of is that some horses (and some people, for that matter), because of their unique chemistry, are naturally more attractive to flies.
So, if a certain repellent seems to work great on your friend’s horse but not on yours, it just might be that flies are repulsed by the natural odor of your friend’s horse and attracted to the natural aroma of your horse.
Some natural horse fly sprays are safe enough to be used on people. However, most chemical fly sprays and gnat creams for horses are not recommended for use. Study labels carefully.
Many repellents carry warnings.
Some chemicals in fly sprays are extremely toxic to fish, perhaps because they are metabolized and eliminated much more slowly by fish than by mammals. When you’re disposing of or washing fly spray containers, be careful not to contaminate fish-bearing waters.
The number and strength of these precautions should make you aware that insect repellents should be used with discretion and kept out of the reach of children. Be especially careful of applying a product containing insecticides around a nursing mare’s udder because a foal might ingest the product and get it in his eyes.
Some products can be used on minor scratches, but very few are recommended for applying directly to wounds.
Pyrethrins are natural insecticides derived from chrysanthemum flowers. They are the most common, and arguably the safest, insecticides used in fly sprays. Some characteristics that make pyrethrins safe are also their failing: they decompose quickly in light and air and have very little residual effect. Direct skin contact or inhalation of pyrethrins may cause severe allergic attacks in sensitive people, especially those with a history of allergies or asthma.
Pyrethrins are nerve poisons that work by quickly paralyzing the nervous system of an insect, either when ingested or contacted. They kill adults, eggs, and larvae.
Pyrethroids are synthetic chemicals that act like natural pyrethrins. These compounds are more stable in light and air than pyrethrins, so have a much longer residual effect, some lasting for weeks. Pyrethroids are extremely toxic to bees but only slightly toxic, if at all, to birds. They aren’t as likely as pyrethrins to cause allergic reactions, but they can cause varying degrees of skin irritation.
Permethrins are the most common pyethroids in insect repellents. They are also used as a tick repellent spray for clothing (not skin) to prevent spread of Lyme disease.
Cypermethrins are popular products used for spot treatment control of insects, such as in cracks and crevices.
Resnethrin has an odor characteristic of chrysanthemums. Unlike other pyrethroids, it breaks down quickly in the presence of light and humidity so fly spray containing resnethrin should be kept tightly sealed in an opaque container.
The repellents in natural fly sprays are derived from herbs such as lavender and pennyroyal, the chrysanthemum flower, and trees including eucalyptus, tea, pine and cedar.
Citronella is the most well-known natural repellent. It is a pleasant smelling oil derived from lemon grass. Citronella is a repellent, not an insecticide, so don’t expect flies to drop dead when you spray them.