About 150 species of snakes occur in North America, of which over 90% are non-venomous. All native snakes are very beneficial members of the biota. Rattlesnakes, copperheads, cottonmouths, and coral snakes are native to the US and venomous. All venomous snakes in North America, except coral snakes, belong in a group called pit vipers.
Snakes are considered nongame wildlife and are protected by law in most states, unless they are about to cause damage to persons or property. Snakes should never be killed indiscriminately. Some species are listed on federal and state threatened and endangered species lists.
People commonly call dangerous snakes, such as rattlesnakes, “poisonous.” The correct term is “venomous.” Venom is a toxic substance that is injected into a victim. It primarily is used to secure prey. Poison refers to a toxic substance that is ingested (swallowed) by a victim and usually is used as a defensive tool. Plants have poison, but spiders and snakes use venom that is injected through a bite with toxins and enzymes.
Snakes are specialized animals with elongated bodies and no legs. They have no ears or eyelids, but transparent scales cover the eyes. Organs of snakes are elongated. Snakes have a long, forked tongue, which aids the sense of smell. Particles from odors are picked up by the tongue and inserted into a 2-holed vomeronasal organ in the roof of the mouth.
The 2 halves of the lower jaw are not fused, but are connected by a ligament. The configuration of the jaw allows snakes to swallow food much larger than their heads. Snakes are ectothermic (cold-blooded) and may consume only 1 meal in several weeks. Snakes may hibernate during cold weather or aestivate during hot summer months. Snakes consume little or no food during times of decreased activity.
Snakes vary in length, depending on age and species. Scientists typically measure a snake from the tip of the snout to the vent (cloaca opening), as tails may be damaged. Color usually is not a primary indicator for the identification of snakes. Coloration can vary greatly by area, genetic variation, and age of the snake.
Use these features to identify snakes:
- The keel is a ridge that runs along the middle of the scales in some types of snakes. Like the keel of a boat, the ridge may be pronounced, less pronounced, or absent. Rub a finger across the width of the skin of the snake to feel for the presence of a keel.
- Inspect the vent. Check if the scale that covers the vent is divided or single.
- Unlike color, patterning can be helpful for identifying snakes, although in some species the pattern of juveniles differs considerably from adults. Identify whether the snake has stripes, blotches, or solid coloration.
- Snout to vent length may be helpful but can be misleading in small snakes.
- Number of scales across the width of the snake.
- Check if the head scales are large or small.
Pit Vipers versus Non-Venomous Snakes
Several characteristics can be used to distinguish between pit vipers and non-venomous snakes. All pit vipers have a deep pit on each side of the head, midway between the eye and nostril. Non-venomous snakes do not have pits.
On the underside of the tail of pit vipers, scales typically (but not always) go all the way across in 1 row. On the underside of the tail of most non-venomous snakes, scales are in 2 rows all the way from the vent of the snake to the tip of the tail. The shed skin of a snake shows the same characteristics. Since exceptions to the rule exist, do not use this technique to conclusively differentiate between venomous and non-venomous snakes.
The pupil of non-venomous snakes is perfectly round. The pupil of pit vipers is vertically egg-shaped. In very bright light, the pupil may be a vertical line due to extreme contraction to shut out light.
Coral snakes are venomous and ringed with red, yellow, and black, with the red and yellow rings touching. Non-venomous mimics of coral snakes, such as the scarlet king snake, have red and yellow rings separated by black rings.
A helpful saying is “red on yellow, kill a fellow; red on black, friend of Jack.” The saying is useful only in the& US and Canada. It does not apply to snakes in Mexico.
Consult field guides of snakes for information on the range of a specific species. State-specific guides to snakes also can be helpful.
Voice and Sounds
Some snakes, such as bull snakes, may hiss in a manner that sounds like a rattlesnake. Hognose snakes will puff. Many snakes shake their tails, which can sound like a rattle.
Tracks and Signs
Snakes rarely leave signs of their presence. It takes a careful eye to notice disturbances in soil that indicate the movement of snakes. Skins of snakes are sometimes found in attics and crawl spaces. Look for paths in dust, drags through spider webs, and skins that have been shed. Skins shed by snakes tend to be 20% longer, on average, than the total length of the snake that shed it.
Information on this species is based on the chapter in Prevention and Control of Wildlife Damage (Hygnstrom, Larson, Timm, ed. 1994), written by James Byford (University of Tennessee) and Walter E. Howard (University of California, Davis).