Most dangerous snakes are venomous, meaning they inject toxins via specialized fangs when biting or stinging. A truly poisonous animal delivers toxins passively, such as when the substance is ingested or absorbed through touch. While a few snakes sequester toxins from their diet, the primary concern for human safety involves the approximately 600 venomous species globally. Identification should always be done from a safe distance. The physical characteristics described here are general guidelines, not infallible rules, and should never be used as an invitation to approach or handle a snake.
General Physical Indicators of Venomous Snakes
The most widespread group of venomous snakes in North America are the pit vipers, including rattlesnakes, copperheads, and cottonmouths. They share several distinct features, starting with a broad, triangular head that is significantly wider than the neck. Non-venomous snakes usually have a rounded head that flows smoothly into the body, though some harmless species flatten their heads when threatened, mimicking the pit viper shape.
Pit vipers generally exhibit elliptical pupils, resembling vertical slits. Most non-venomous snakes in the same regions possess round pupils, though this is difficult to observe safely. Pit vipers are also named for the loreal pit, a small, deep indentation located between the eye and the nostril. This heat-detecting organ allows the snake to locate warm-blooded prey. Relying on any single trait, such as head shape, can lead to misidentification due to non-venomous species that mimic these features. Color and pattern are also highly unreliable for identification, as they vary widely even within the same species.
Identifying Elapids: The Exceptions to General Rules
The family Elapidae, represented in North America by the coral snake, is an exception to the pit viper rules. Coral snakes have small, narrow heads that are not distinct from the neck, and they possess round pupils. Their venom is a potent neurotoxin, contrasting with the hemotoxic venom common to pit vipers.
Identification relies on the distinct color pattern of alternating red, yellow, and black bands. Numerous non-venomous snakes, such as the scarlet kingsnake, exhibit similar coloring (Batesian mimicry). The distinction in the United States is often summarized by a traditional rhyme: “Red on yellow, kills a fellow; Red on black, friend of Jack.”
In the venomous coral snake, the red bands are always bordered by yellow bands. In the harmless mimics, the red bands are bordered by black bands. This mnemonic should be applied only in regions where it is known to be reliable, as it is not universally accurate for all coral snake species outside the U.S.
Habitat, Behavior, and Movement Clues
A snake’s location and actions can provide clues beyond physical appearance. Pit vipers are often found in environments that provide cover for ambush, such as rocky outcrops, wooded areas, leaf litter, and brush piles. Cottonmouths are semi-aquatic and frequently found near swamps, lakes, or slow-moving streams, often floating with their heads slightly raised.
When disturbed, venomous snakes are defensive, preferring to avoid confrontation. Rattlesnakes often vibrate the keratinous segments of their tail to produce a warning sound, though they may strike without rattling if startled. Copperheads may freeze and remain motionless, relying on camouflage. Cottonmouths may coil and display the bright white interior of their mouth as a threat display.
Movement patterns are generally unreliable for identification, as all snakes use variations of undulation or concertina movement. However, heavy-bodied pit vipers often appear slower and more deliberate than slender, fast-moving non-venomous snakes. The safest approach is to assume any unidentified snake is venomous and maintain a distance of at least twice its estimated body length.
Immediate Safety Measures After an Encounter or Bite
If a snake bite occurs, the most important action is to seek professional medical attention immediately by calling emergency services. While waiting for help, the victim should remain calm and still, as an increased heart rate accelerates the spread of venom through the circulatory system. Remove any jewelry or tight clothing near the bite site before swelling begins.
The bitten limb should be immobilized and kept in a neutral position, ideally at or slightly below the level of the heart to slow venom circulation. The wound should be gently cleaned with soap and water and covered loosely with a clean, dry dressing to reduce infection risk. Safely photograph the snake from a distance for medical personnel, but never attempt to capture or kill the animal.
It is important to know what actions to avoid, as many traditional first-aid methods are ineffective or harmful.
Actions to Avoid
- Applying tourniquets, which can cause severe tissue damage by restricting blood flow.
- Using ice on the wound, which can also restrict blood flow and cause damage.
- Attempting to cut the wound or suck out the venom, as this does not remove a meaningful amount of venom and introduces bacteria.