Use herbs and essential oils for natural insect repellents and bug bite remedies.
A supplement to The Herb Companion from the American Botanical Council and the Herb Research Foundation.
Aphids, whiteflies, spider mites, leaf-munching caterpillars. Herb gardeners know these plant pests all too well. But you don’t need to be a gardener to have close—frequently unpleasant—encounters with a whole array of other annoying outdoor insect and arachnid pests.
To distinguish which kind of critter you’re dealing with, just remember: insects have six legs, arachnids, eight. Mosquitoes, fleas, and flies (which are insects), as well as ticks and chiggers (which are arachnids), are biters. Most of these are after your blood. Many of them need a protein meal so that they can lay eggs. Bees, wasps, hornets, and ants (insects all) are stingers. Some kinds of ants both bite and sting. If you spend much time outdoors, bug bites and stings are inevitable. Most cause only transient local pain and/or itching, but about 1 percent of Americans experience severe allergic reactions to insect venom; about fifty die each year.
Furthermore, these pests can transmit diseases. Mosquitoes can carry malaria, yellow fever, or encephalitis; tick-borne Lyme disease and Rocky Mountain spotted fever are known throughout much of the United States. Your local newspaper and television station will surely let you know if any insect- or tick-borne diseases are prevalent where you live and what measures you should take to deal with them.
These pests can make gardening during the warm months disagreeable; when they’re really bad, they can drive you indoors. The first line of defense is prevention. Most people do attempt to stay out of the way of stinging insects, and most of them won’t bother you unless you bother them first. A repellent can deter parasitic bloodsuckers such as mosquitoes, blackflies, deerflies, and horseflies, which attack uncovered skin around the hands, face, neck, and legs. Scientists have tested thousands of substances, including hundreds of plant essential oils, for their insect-repellent potential. Those of pennyroyal, cedarwood, citronella, and eucalyptus are the most commonly used in insect repellents.
The essential oil of European pennyroyal (Mentha pulegium) has the strongest reputation as an insect repellent. The specific name, pulegium, is derived from the Latin pulex, meaning “flea”, and refers to the plant’s reputed ability to kill fleas. The Roman historian Pliny wrote of pennyroyal: “The blossom of it, fresh gathered and burnt, kills fleas by its smell.”
Pennyroyal also has long been used to deter mosquitoes, mites, ants, and ticks. Pulegone, a compound that constitutes as much as 85 percent of the oil, appears to repel ants and other insects that live near the plants. Studies have shown that it kills several kinds of insects, but its effectiveness depends on both its concentration and the tolerance of the organism.
I have found that oil of European pennyroyal or that of its cousin, American pennyroyal (Hedeoma pulegioides), dabbed onto pant cuffs, sock tops, and sneakers, deters ticks and chiggers in the Arkansas Ozarks. Unfortunately, it seems to attract mosquitoes.
Cedarwood oil is derived from several species of junipers, including eastern red cedar (Juniperus virginiana), the wood of which is used to make cedar chests, and the southwestern alligator juniper (J. deppeana). The oil, obtained by steam distillation of sawdust, shavings, and other lumber wastes, is used as a fragrance and fixative in cosmetics and household products. Few studies have evaluated the oil’s effectiveness as an insect repellent or insecticide, but a 1952 study reported that 91 percent of the half-grown moth larvae exposed to the oil for one week in a closed cedar chest died. The oil used to be widely used in commercial insect repellents but is seldom used today.
The essential oil of citronella (Cymbopogon nardus), a plant similar to lemongrass (C. citratus), is widely used in natural insect repellents, including candles, although its effectiveness has not been confirmed by scientific tests. I have encircled captured ticks in droplets of the oil and watched them do back flips when they moved close to the oil. This crude experiment convinced me to continue to apply the oil to my shoes and pant cuffs before going into the woods during tick and chigger season.
The strongly aromatic essential oil from the leaves of the common eucalyptus known as blue gum (Eucalyptus globulus) was often an ingredient in insect repellents in the past. Although no substantial scientific data support its effectiveness, the trees have a reputation of not being subject to insect attacks.
Use any of these essential oils with caution: direct skin contact may cause contact dermatitis or chemical burns. I find that they work best applied to clothing.
Witch hazel (or hamamelis) water, a distillate of the twigs and leaves of Hamamelis virginiana, is approved by the Food and Drug Administration as an over-the-counter remedy for alleviating the itch and inflammation of insect bites. It is widely available at pharmacies.
Herbal lotions or creams containing calendula (Calendula officinalis) or chamomile (Matricaria recutita) can soothe bug bites or a mild sting. Both have been shown to reduce inflammation and encourage healing. I find that calendula lotions take the itch out of chigger bites, as do ointments high in essential oils, such as tiger balm.
Poultices of the fresh leaves of English and broad-leaved plantain (Plantago lanceolata and P. major) also offer relief from insect bites. Although no scientific evidence supports anecdotal reports of a plantain poultice’s successfully treating severe reactions to insect stings, I have found that fresh plantain leaves reduce the pain and swelling of ordinary insect stings if applied immediately.
Being familiar with the habits of insect adn arachnid pests and their modes of attack can help you cope with them.
Mosquitoes are one of the most annoying groups of biting insects. Of 3,000 species in the world, 160 live in the United States. Fortunately, not all of them feed on humans.
Most mosquitoes lay their eggs on the surface of water, but some deposit eggs at the water’s edge, relying on flooding to make them hatch. The larvae live in water; the first line of defense against mosquitoes is to eliminate standing water. This includes the water in watering cans, old tires, flowerpot saucers, and other containers in which water collects.
It is the females that cause all the trouble, from the human point of view. When a female mosquito alights on your skin, she inserts her proboscis, a needlelike, flexible hollow tube, to suck your blood. The anticoagulants and other toxic substances that she injects while feeding are what cause itching. Some mosquitoes carry diseases such as malaria, yellow fever, and encephalitis.
These tiny insects—about 2,000 species worldwide—are found from the warm, humid Tropics to the Arctic. Cat fleas (which also attack humans) are the ones you’re probably most familiar with. Adult fleas emerge from cocoons in response to heat and exhaled carbon dioxide of a warm-blooded host. Both sexes immediately seek a blood meal. They usually bite humans on the legs and ankles, injecting saliva to prevent clotting. Reaction to the saliva can cause swelling and intense itching. Some fleas carry bubonic plague and endemic typhus.
The small, humpbacked demons known as blackflies are notorious in northern North America in June, but they actually occur throughout the United States and are at work all summer. The larvae live in flowing streams, but the adults can be blown many miles from their breeding sites—to your yard, for example. They are so light that often you don’t feel them land, but their voracious bite certainly lets you know they are there. The bites can swell and itch for several days.
Biting midges, also called no-see-ums or sand flies, are annoying flies that are small enough to pass through window screens. They are most common in coastal areas. Their bites can itch for several days.
Deer- and horseflies pack a painful bite. The female horsefly has an anticoagulant in its saliva, and its bite can bleed for several minutes. Some deerflies carry tularemia.
Honeybees, bumblebees, hornets, wasps, and velvet ants (actually a kind of ground-dwelling wasp) are common stinging insects. The honeybee is unique among insects in North America in that its barbed stinger and venom sac pull out of its body when it flies off after it stings; it soon dies. Meanwhile, the stinger, if not removed, will work its way deeper into your skin. Scrape or pull it out as soon as possible. Pulling, once discouraged because it was thought to inject more venom, has recently been judged effective as a method of removal. Yellow jackets (a kind of wasp), by contrast, have smooth stingers that they can use repeatedly.
More than 4,000 species of wasps occur in North America. Only the females sting. The two barbed shafts (lancets) of the stinger alternately work deeper into the victim until the poison duct between the lancets opens and injects the venom. Wasp stings are always painful and in sensitive individuals can cause anaphylactic shock: severe swelling, dizziness, difficulty breathing, even death.
Velvet ants are widely distributed in open, sandy areas of the South and West. Only the females sting; in one species found in much of eastern North America the stinger is about half the length of the 1-inch body. Female velvet ants have been dubbed cow killers on account of the severity of their stings, which cause acute pain (usually of short duration) and swelling that may last several hours.
Several species of fire ants occur in southern North America. The females can inflict both a painful bite and sting. If you step on a fire ant mound, the ants cling and may be difficult to brush off. Females first bite, then insert their stinger one or more times, causing local pain, swelling, itching, and pustules that may persist for weeks. A single ant sting can cause anaphylactic shock in sensitive individuals. Harvester ants, found in the South and Southwest, also have a painful bite and sting.
Ticks and chiggers are arachnids, related to spiders. Ticks feed on the blood of humans and wild and domesticated animals. Be careful when you remove them: specialized mouthparts that hold them tightly to your skin can remain in the skin, causing itching or even nodules. Grasp a tick carefully with tweezers or between your fingernails and pull it steadily outward. Covering attached ticks with fingernail polish or kerosene to induce them to let go is no longer recommended. In recent years, deer ticks have become a serious problem in some areas because they carry Lyme disease.
Chiggers are tiny red mites common in lawns and brushy areas, especially in the South. They lay their eggs on the ground. The near-microscopic larvae climb up grass blades and move onto anyone who passes by. They attach to the skin and secrete a fluid that liquefies cells in the immediate area and apparently causes the underlying tissue to form a tube through which they suck fluid containing the digested cells. The bite becomes an intensely itchy red welt that may measure 3/4 inch across and not disappear for several weeks; itching may persist intermittently.
Foster, S. Herbal Renaissance. Layton, Utah: Gibbs Smith, 1993.
Herbs for Your Health. Loveland, Colorado: Interweave Press, 1996.
Foster, S., and R. Caras. A Field Guide to Venomous Animals and Poisonous Plants. Boston: Houghton Mifflin, 1994.
Sadik, F. “Insect Sting and Bite Products”. In Handbook of Nonprescription Drugs. 11th ed. Washington, D.C.: The American Pharmaceutical Association, 1996.
“Herbs for Health” is offered bimonthly by the American Botanical Council and the Herb Research Foundation as a supplement to The Herb Companion.
Editor, Steven Foster
American Botanical Council
PO Box 201660 Austin, TX 78720
Herb Research Foundation
1007 Pearl St., Ste. 200 Boulder, CO 80302
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