Snake Repellents: How--and How Well--Do They Work?

The most easily obtained snake repellent on the U.S. market today uses a mixture of naphthalene crystals and sulfur granules. That product, which relies on the interference of its ingredients with the snake's Jacobson's organ, has been tested by a number of authorities, including at least one university, and found to reliably repel a wide number of snake species, including most rattlesnakes, in particular when these snakes are performing random searches for prey at ground level.  However, besides being mildly toxic, and lacing your clothing with an objectionable odor that lingers for hours after applying it, no naphthalene/sulfur based product has been found to reliably repel those snakes that are attracted to, and that consume, decaying flesh. This seems to result from the fact that the chemicals produced during putrefaction are similar to the repellent's constituent ingredients.

Unfortunately, all the copperheads, cottonmouths, and non-venomous water snakes in the genus Nerodia, fall into that latter grouping. Thus, snake repellents based on sulfur and naphthalene perform poorly at repelling some of the most common, dangerous (copperheads and cottonmouths) and annoying (nerodian water snakes) serpents around.

Soon after learning of this serious gap in the performance of naphthalene/sulfur snake repellents, I began a long-term, on-going investigation into the various alternatives available, hoping to find a repellent that would repel snakes of all species. I will be posting the results of that investigation here as time permits. Of course, this gap is common knowledge, and manufacturers of alternative snake repellents see it as a welcome opportunity to aid in marketing their products. As you probably already know from your own Internet searches, snake repellents claiming to repel all species of snakes are presently being marketed on the Internet under a number of brands.

The important thing to realize about those alternative snake repellents is that few or none of them have been subjected to rigorous, scientific testing to determine if, and under what circumstances, they actually work. Most claim to disrupt the function of the snake's Jacobson's organs, much as the naphthalene/sulfur repellents do, but without the disabilities of the latter. Presumably, this accrues from the fact that the strong fragrances associated with the alternative repellents bear no resemblance to decaying flesh. But do these repellents work as advertised? Only a series of well-designed scientific tests will tell for sure, and such testing is so expensive and time consuming that it exceeds the budgets of most of the repellent manufacturers.

Beyond that question, however, lies another whose importance should not be ignored: just how crucial is the Jacobson's organ as a determinant of where a snake will or won't go?

Many snakes prey on birds and their eggs, and on arboreal rodents such as squirrels. These snakes, including but not limited to the colubrid rat snakes in the genus Elaphe, often travel considerable distances aerially, from tree to tree without ever touching the ground where repellents have been applied. Though some repellents can be applied to trees, wholesale arboreal treatments with snake repellent is almost never practicable. Thus, a yard that is blessed with numerous trees with interconnected crowns will likely be visited regularly by arboreal serpents regardless of the repellents that are applied under them.

Likewise, all snakes spend part of their lives underground. Many live underground exclusively; and some of our most dangerous serpents prefer to hunt for prey under the ground rather than above, when given a choice. Subterranean passages are often intricately connected together in a labyrinthine maze of immense proportions, and such passages may abound beneath many yards without any overt indication of their existence at ground level. The small entry/exit ports at ground level used by the serpents that inhabit such underground passageways may be hidden from view of even the most careful investigator, especially if the landscape--or home situated on that lot--is blessed with low-level wooden decks or similar structures. As a consequence, applications of snake repellent in the traditional manner--around the perimeters of the yard, in the landscaping,. and around outsides of structures, will fail to protect that property from snake incursions regardless of the kind of repellent that is utilized.

Some snakes, notable among them the coachwhips, racers, and whipsnakes, almost never use their Jacobson's organs to hunt prey. Such snakes rely instead on large eyes that offer excellent visual acuity, along with an ability to raise their heads high above the ground as they travel, so they can scan the terrain for lizards and rodents. It is unreasonable to expect such snakes to be repelled by any strong-smelling granules or sprays, especially when they are visually tracking prey.

Of course, when good, field-tested snake repellents are used in conjunction with a good snake exclusion program, as described on a separate page, incursions of snakes within the treated yard and home may drop considerably, often to the point that the human residents rarely or never see a snake. Even in such locales, however, an unpleasant surprise may pop up from time to time, in quite unexpected places. Several times a year I receive reports of snakes inside homes, most often in bathrooms.  Such snakes easily enter these homes via the sewer system, usually but not always via a commode. Sewers provide excellent habitat for most serpents. Water, in the p-trap of a sink or commode, is not an effective barrier to snakes. I am surprised, in fact, that such reports are not more numerous. Thinking on this, I have yet to come up with any effective remedy that will guard against snake incursions from the sewer.

In conclusion, the efficacy of a particular snake repellent cannot be assured without considerable evaluation and testing that takes place over a period of several years. Besides that, even a highly effective snake repellent cannot prevent aerial incursions from arboreal snakes in heavily forested yards whose trees have interconnected crowns. The same caveat applies to yards underlain with subterranean passageways. And, last, even the most thorough snake exclusion program will be defeated, from time to time, by serpents that enter the home from a sewer connection. I realize that this is more information than many, especially those who are deathly afraid of any snake they see, can or want to digest. What it points to, however, is not so much that snakes are inevitable, but that those who are determined not to see any in their yards or homes are well advised to learn and follow the advice I and others provide on snake exclusion.

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