Herbs vs. Bugs

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Lemon oil is rich in the lemon-scented limonene. Limonene is documented as lethal to the cat flea and is sometimes marketed as a “natural” dip. While lemon and other citrus oils are indeed natural, toxic reactions and even deaths have been reported in dipped cats. Most self-respecting cats do not wear clothing, so soak bedding and pillows with lemon oil as a safer alternative to dipping.

Pennyroyal, a creeping perennial mint, is the herb best known for flea repellency. The first-century Roman scholar Pliny noticed its effectiveness against fleas, as did the eighteenth-century Swedish botanist Linnaeus, who named the plant Mentha pulegium, from the Latin word for flea, pulex. Native American Indians rubbed leaves of American pennyroyal (Hedeoma pulegioides) onto their skin as protection from insects. I find no good scientific studies on the repellency of pennyroyal or its primary constituent, pulegone, yet the anecdotal evidence is so rich that I feel they should be explored.

A word of caution about the use of pennyroyal: at least one woman has died from ingesting an ounce of pennyroyal oil, and rats have displayed brain degeneration after being dosed with it. So don’t drink pennyroyal tea or oil, or even apply it to your skin or your pets. Pennyroyal pillows to tuck into your dog’s or cat’s bed have produced no reported problems, however, and may actually work.

Another plant widely recognized as a flea repellent is fleabane (Conyza canadensis). Mrs. M. Grieve, in A Modern Herbal, states that if fleabane is burned, its smoke will drive off fleas and other insects. Cul­peper says, “The smell is supposed delightful to insects, and the juice destructive to them.” Gerard, in his Herball, has another idea on how this plant got its name: “I thinke it is rather because the seed doth resemble a flea so much, that it is hard to discern the one from the other.” Chemical studies of the essential oils of fleabane have been published, but I know of none that address its insect repellency.

The Indians of Mendocino County, California historically used California laurel (Umbellularia californica) to repel fleas. The leaves of Boenninghausenia albiflora, a perennial herb of temperate India, have a disagreeable odor and a long reputation as an effective repellent of fleas; Indian scientists who tested the oil against the dog flea report that it works well. Another plant that may be repellent to fleas is vitex (Vitex negundo).

Tick

Oh, how I wish that I had a safe repellent of the deer tick, which carries Lyme disease, or a good repellent for the wood tick and the American dog tick, both of which carry Rocky Mountain spotted fever. The fear of these diseases has severely curtailed my field trips in the woods and swamps.

Opopanax or bisabol myrrh (Commiphora erythraea) is the subject of the only good scientific tests on natural tick repellency that I can find. This myrrh of the ancient Egyptians has been recently documented as killing the larvae on contact and repelling the adults of African brown ear tick, deer tick, lone star tick and American dog tick. Does the oil of the more readily available common myrrh (C. myrrha) likewise repel ticks? I put it in my ­formula because I thought it was worth a try.

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