Biology and Behavior
Snakes are members of the class Reptilia, commonly known as the reptiles. This class is comprised of four orders:
- Squamata (lizards and snakes)
- Crocodylia (alligators, crocodiles, and caimans)
- Testudines (turtles, tortoises, and terrapins)
- Rhynchocephalia (tuataras)
A common trait shared among reptiles is that the body is covered by scales that, in some species, shed periodically. The frequency with which snakes shed this outer layer is determined in part by age, physical condition, and amount of food intake. Actively growing younger snakes generally shed the outer skin once every two to three months, whereas mature adults may shed only once or twice a year.
Another characteristic of reptiles is that they are described as being cold-blooded, which means they are unable to internally regulate their body temperature; therefore, they are influenced strongly by the temperature of the environment in which they exist. In other words, on cool or cold days, reptiles may seek warm shelter to increase their body temperature, whereas on warm or hot days, they must find cool areas to avoid overheating. Hence, their behavior and movements often are dictated by the need to adjust body temperature in response to prevailing environmental conditions, an adaptation referred to as “behavioral thermoregulation.” This explains why you often see snakes basking in the sunshine on cool mornings as a way to warm up, but hiding in the shade of landscape plants or in a cool basement or spring house during the heat of the day.
Virginia is home to 30 species of naturally occurring snakes. Of these, only three species are classified as being venomous:
- Copperhead (Agkistrodon contortrix), figure 1, which has statewide distribution.
- Timber rattlesnake (Crotalus horridus), figure 2, which is restricted to the western one-third of the state and a very small portion of extreme southeastern Virginia (as the canebrake rattlesnake, a subspecies of the timber rattlesnake).
- Cottonmouth (Agkistrodon piscivorus), which is restricted to the lower southeastern Coastal Plain only.
Of the 30 native species, only about 10 occur statewide; many of the other species are relatively uncommon or have restricted ranges. As a general rule of thumb, a greater number of species occurs in the southeastern Coastal Plain than anywhere else in the commonwealth. Useful information about the distribution of snakes within Virginia, including range maps, can be obtained from the website of the Virginia Herpetological Society (http://www.virginiaherpetologicalsociety.com) and from the Virginia Department of Game and Inland Fisheries’ brochure, “A Guide to the Snakes of Virginia” (see Recommended Reading).
Egg-Laying vs. Live-Bearing
Snakes display different approaches to producing their young: those that lay eggs (oviparous) and those that bear live offspring (viviparous).
Among the species that lay eggs, egg-laying generally occurs during late spring or early summer, and the new hatchlings emerge anywhere from mid-summer to early fall. The female produces eggs that are somewhat leathery and flexible and have a well-developed yolk sac that provides nourishment to the embryo. The female deposits her eggs (anywhere from 2 to 50 per nest, depending on the species; the mudsnake may produce up to 100) in a mulch pile, under decomposing leaves, or beneath logs or other organic debris where warmth is generated as the material rots. Once the eggs are laid, there is no further contact between parent and offspring. Ratsnakes, green snakes, and milk snakes are examples of species that deposit eggs.
However, not all snakes deposit eggs in the environment. In many species, the female retains the developing young within her body until the fully developed young snakes are ready to exit. There are differences among species regarding the internal physiology associated with livebearers and the degree to which nutritional support is provided maternally (i.e., across the placenta).
Some researchers recognize a distinction between full-placental provision, or “viviparity,” and incomplete or partial placental provisioning, or “voviviparity.” For simplicity, it is much easier to treat all the species in this group as simply livebearers. The three prominent venomous snakes in Virginia — copperhead, cottonmouth, and timber rattlesnake — all produce live young, as do all watersnakes, the garter snake, and the ribbon snake. Similar to what is characteristic of egg-laying species, parental care is not provided by the adults in live-bearing species after the young emerge; they are entirely on their own from birth.
Given the diversity of reproductive strategies that snakes display, it should be obvious that one of the more common myths about snakes — that a venomous and a nonvenomous snake (for example, an eastern ratsnake, figure 3), will interbreed and produce venomous offspring that resemble a ratsnake — cannot be true. In addition to being completely different species, their differing reproductive physiologies prevent them from producing viable offspring.
Snakes use all the senses they possess to engage with their environment, but they rely most heavily upon their senses of smell and touch (i.e., their ability to detect vibration through the body). Although some snakes do see well, that capability is restricted mostly to short distances, especially when they are about to shed their skin. At that time, the normally clear scales that cover the snake’s eyes cloud over and make seeing more difficult.
Snakes lack the physiological structures (no inner ear chamber or ear drum) that would enable them to hear in the way that humans and most other animals do; however, “hearing” still plays an important role in how snakes gather information about their environment. Because a large proportion of a snake’s body is in direct contact with the ground or other surfaces, vibrations transmitted through those substrates pass directly to the snake, alerting it to the approach of potential prey or danger. Once alerted, the snake refines the initial signals it receives using smell.
However, snakes do not sniff the air with their noses, as other animals do. Instead, they extend and wave their forked tongue to collect chemical “air samples,” which then are deposited in special cavities located on the roof of the mouth, called “Jacobson’s Organ.” The chemical scents collected from the air are interpreted or decoded by receptors in these cavities.
In addition to using touch and smell, the pit vipers (e.g., cottonmouth, copperhead, and rattlesnake) possess special heat-sensing organs known as “loreal pits” (figure 4), located on each side of the head just forward of the eyes, that help them detect and track potential prey.
For an animal with no legs, one might suspect that moving from one spot to another would be challenging for a snake. However, if you have ever witnessed how fast they can move, you realize that snakes have successfully adopted other means of movement.
Snakes use one of three methods to propel themselves on land: (1) arching the body into an open “S”-shape and using the lateral muscles to push off against vegetation or irregularities on the ground, (2) coiling the body into a series of tight curves and pushing off or springing forward against its own body mass, or (3) sequentially raising and lowering the scales on its belly in an undulating fashion to push forward using the traction gained by the scales gripping the ground.
They use the same undulating “S”-shaped movement to swim.
If you corner a snake and provide it with few options of escape, the snake very likely will coil up into a tight mass and prepare to defend itself, often by striking out at the entity that approaches too closely. In such a situation, a frequently asked question is, “How far can a snake actually lunge if it was to attempt to strike out at me?” The answer will vary depending on the age and size of the snake, and, to some extent, on the species involved. A relative rule of thumb is that most snakes are capable of lunging a distance equal to about one-third to one-half of their total length.
Many people openly question the value of snakes, a perception that reflects the personal fear many folks have of snakes and the way our culture historically has viewed these animals. A vast amount of misinformation, myths, and folklore has been spread about snakes and, unfortunately, much of this helps to maintain the negative image people have of snakes in general. Although venomous snakes occasionally may pose a risk to one’s personal health and safety, the vast majority of species do not present an imminent danger or threat to us. Yet they have suffered significant losses — primarily due to people’s lack of familiarity with and unfounded fear of them.
The larger species of snakes provide an important service by helping to manage rodent populations (e.g., rats, mice, and voles) that can cause serious economic problems for homeowners, farmers, and businesses. In fact, farmers used to pay local kids a small “reward” to go out and collect ratsnakes to release around the barn and farmyard as a way to keep rodents in check. Many of the smaller species feed on insects and other invertebrate pests common to our gardens and landscape plantings.
Although some species of snakes will prey on small songbirds or consume the birds’ eggs where that opportunity exists, many snakes serve as a food resource for other predators, such as raccoons, opossums, skunks, birds of prey, and even other snakes. Thus, snakes are important players in the food web and therefore are a key component of a healthy ecosystem.
Snakes in a Residence, Business Setting, or Other Occupied Space
There may be nothing more startling or unsettling to some folks than finding a snake crawling along the baseboard of a room in one’s home or finding a shed snake skin in the cellar, bedroom closet, or attic — a clear indicator that a snake has been in the building. Not knowing where the snake is currently or whether it has left the site is enough to drive some people out of the building until they can be assured it is “all clear.” To many folks, this is a violation of their personal living or working space.
Snakes enter a building for several primary reasons. In many cases, they simply were following and hunting their preferred food item (mice), which also happened to be sharing our living space. In other cases, snakes may be seeking a secure location to lay eggs. Snakes sometimes enter a building seeking conditions that will help them shed their old skin (small openings or sharp angles provide useful wedges to help peel off the old skin). Finally, a snake may seek temporary shelter from a predator or to help regulate body temperature.
Regardless of why a snake may have entered a residence or work area, most people just want to know how to remove it. However, people confronted with a snake must understand that under existing wildlife regulations, it is illegal to kill any species of snake in Virginia unless it presents an imminent threat to one’s personal health and safety.
Snakes are classified as nongame species and therefore are afforded full protection under existing nongame regulations, similar to all other species in this category. In the case of the canebrake rattlesnake, which is one of Virginia’s state-listed endangered species, neither the animal nor its habitat can be destroyed.
Thus, trying to kill any snake found in the home is not an appropriate solution. Instead, homeowners should concentrate on eliminating the attraction that brought the snake to the home in the first place and closing all points of access that allowed the animal to enter. The following serve as useful steps for homeowners to consider:
- Eliminate the prey population that snakes are looking for by removing or cleaning up food resources in the home that attract and support rodents. This would include things like spilled bird seed, accessible pet food stores, open containers of dry goods, and similar potential food items. Transfer all stored dry goods to metal or glass containers that cannot be chewed by rodents.
- Repair, seal, or close off any openings 1/4 inch or larger that provide animals with access to the interior of the building. Most rodents need an opening of only 1/4 inch in size, or access to an opening that they can enlarge by gnawing, to get into the home. Places to concentrate your initial search efforts would be where utility service (e.g., water, sewer, electric, telephone, cable) enters the home; where the clothes dryer vent exits the building; around doors, windows, and bulkheads to the basement or garage (including the gap under a large garage door); and where the house sits on its foundation (the sill area). Remember, if a rodent can get in, so can a snake — often by using the very same openings.
- Thin or reduce the amount of landscape plantings that exist immediately against the foundation of the home. Thick, lush gardens and layers of growth located against the home provide perfect cover and protection to both snakes and their prey. Further, thick plantings provide these animals with time under protective cover to look for new ways to get in without having to worry about being exposed or vulnerable.
If you should find a snake in the home, removal can be accomplished most easily by using long-handled implements, such as a flat-bladed shovel, scoop, or broom, to pick up the animal or sweep it into a deep container that has been laid on its side. It is possible to scoop up some snakes with a large-bladed shovel and physically carry them outdoors.
Individuals who have experience in handling snakes may be able to catch a nonvenomous snake by grabbing it immediately behind the head and carrying it outside. Wear gloves and a long-sleeved garment to reduce the likelihood of sustaining a bite. If there is any uncertainty about the identity of the snake, do not attempt to catch it.
If a snake is suspected to be present, but is not immediately evident — or has gone into hiding before capture was possible — several options exist for homeowners. Snakes often will seek cover where warmth and humidity exist, such as around large appliances (e.g., washers, dryers, freezers, hot water heaters, or furnaces) and computers and display monitors. A loosely clumped bath towel that has been lightly dampened and placed near an appliance where a snake is suspected of hiding sometimes will entice the snake to crawl out and move under the towel. If you are ready with capture tools, you often can sweep up the unsuspecting animal as you quickly lift the towel.
A capture device known as a glue board or glue box is available commercially and sometimes can be used to lure a difficult-to-catch snake from the hiding spot. A glue box for snakes is a long, rectangular, cardboard box with an opening at each end and an interior floor that has been coated with a strong adhesive. A snake that enters the box looking for cover becomes entangled in the glue and usually cannot remove itself. For especially large snakes, several rodent glue boards attached securely to a wooden plank and placed against an inner wall may be effective. Glue devices may provide an opportunity to capture and remove a difficult-to-catch animal using other means.
However, never throw a box or a modified glue board that contains a snake directly into the trash. This is a tremendously inhumane act that will result in a very slow death for the animal, and it is illegal.
Further, the people who process your trash might be exposed to potential danger should the animal’s head remain free or it manages to free itself from the device while in the trash receptacle.
Once you have moved the container outside and away from the home, you can easily free the animal by pouring a very small amount of vegetable oil over the surface of the glue to neutralize its stickiness. The snake will be able to wriggle itself free.
Snakes in a Yard, Activity Area, or Public Space
The most effective way to minimize or prevent a chance encounter with a snake outdoors is to modify the habitat such that the snake no longer can fulfill its basic life needs easily. Basic life needs, in this case, refer to food, water, cover, and space. By manipulating the habitat around your home, you can make it very difficult for a snake to survive there. Examples of actions that might be taken include:
- Eliminate, remove, or relocate brush piles, refuse, stored building products, stacked firewood, or other materials that may provide useful cover and hiding spots for both snakes and the prey species they hunt.
- Thin out or selectively remove weedy or overgrown patches of vegetation that may harbor small prey animals such as rodents and provide cover for hiding snakes.
- In areas where small children or pets play, keep the grass well-mowed and maintain an expanse of well-cropped vegetation between the play area and the surrounding woods. Snakes usually do not like to be exposed in the open and away from cover.
- To create a snake-free play area, encircle the area to be protected with a fine-meshed (1/8- to 1/4-inch) fence, about 36 inches in height, that has been dug into the ground so that no gaps exist (figure 5). The fence should be supported by stout posts driven into the ground on the inside of the protected area, but angled outward at about 30 degrees. Because of the outward slant of this design, any access gates incorporated in the fence must open inward. Some fencing experts recommend leaving extra fence material at the top of the device such that it can fold over to the outside of the fence and hang loosely at the top as an additional means of preventing the snake from getting over the top. Be sure that no vegetation comes in contact with or close to the fence as it may provide a means for access over the fence. Remember: snakes generally are skilled climbers.
A number of commercially available products have been registered by the U.S. Environmental Protection Agency (EPA) for use as snake repellents. All of the currently registered products contain some combination of pulverized sulfur and naphthalene as active ingredients, and most are offered in a shakable powder formulation. However, research conducted to investigate the effectiveness of these active ingredients in repelling snakes has yet to show any demonstrated success.
In its effort to eradicate the brown tree snake, an especially troublesome exotic snake, from vulnerable Pacific Island ecosystems where it has been introduced, the U.S. Department of Agriculture, Animal Plant and Health Inspection Service, Wildlife Services (USDA-APHIS-WS), has been experimenting to develop a new snake repellent using combinations of unique ingredients. The current formulation being tested contains a mixture of essential oils, including cinnamon, clove, and/or eugenol. Because each of these essential oils is produced commercially as a food-grade product, they are exempt from the federal product testing and registration requirements (FIFRA §25(b); 40 CFR 152.25) of the EPA.
Although field-testing of this new repellent has yet to be completed, early results suggest that such sprays are ineffective when used as an area repellent; repellency appears to be obtained only by direct application on a visible snake. Whether this concoction of essential oils has any repellency effect on snake species other than the brown tree snake has yet to be determined. A technical note on this subject has been developed by USDA-APHIS-WS and is available at www.aphis.usda.gov/lpa/pubs/tn_wmsnakerepellent.html.
Readers are reminded that use of any other nonfood-grade ingredients or “home-brewed” snake repellents made from chemicals for which an EPA product registration does not exist is a violation of federal law.
There are no chemicals or products registered or approved by the EPA for use as a means to kill snakes. Remember, it is illegal in Virginia to kill any species of snake.
Assistance in Removing a Snake
If you are unable or unwilling to attempt the removal of a snake from your home or business, professional wildlife control operators may be available to assist you with this task. To determine who provides this service in your area, consult the list of certified wildlife control operators, listed by county, on the Virginia Department of Game and Inland Fisheries website: www.dgif.virginia.gov/wildlife/nuisance/trappers/.
Related Issue: Treatment of Snakebite
Recommendations on how best to treat someone who has sustained a snakebite have changed dramatically in recent years. Current recommendations for proper treatment, provided by health professionals at the National Institute of Health, can be obtained at www.nlm.nih.gov/medlineplus/ency/article/000031.htm#First%20Aid.
Appreciation is extended to those who reviewed earlier drafts of this document and provided valuable comments and suggestions on improving its content, including Matt Yancey, Jason Fisher, William Hopkins, and Gary San Julian.
Byford, J. L. 1994. Nonpoisonous snakes. In Prevention and Control of Wildlife Damage, vol. 2, ed. S. E. Hygnstrom, R. M. Timm, and G. E. Larson, F15-F19. Lincoln: University of Nebraska.
Linzey, D. W., and M. J. Clifford. 1981. Snakes of Virginia. Charlottesville: University of Virginia Press.
Martof, B. S., W. M. Palmer, J. R. Bailey, and J. R. Harrison III. 1980. Amphibians and Reptiles of the Carolinas and Virginia. Chapel Hill: University of North Carolina Press.
Pinder, M. J., and J. C. Mitchell. 2001. A Guide to the Snakes of Virginia. Wildlife Diversity Special Pub. No. 2. Richmond: Virginia Department of Game and Inland Fisheries.
Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
August 26, 2010