Colorado has a substantial population of nearly 30 native snake species across its diverse landscapes. Only a small fraction of these residents are venomous. The majority of snakes encountered are harmless and play a beneficial role in the local ecosystem, primarily by controlling rodent populations. Understanding their characteristics and behavior is the first step toward safely sharing the environment.
Colorado’s Venomous Snake Species
Only three species of venomous snakes, all rattlesnakes, are native to Colorado. The most widespread is the Prairie Rattlesnake (Crotalus viridis), a pit viper found throughout the plains and foothills. The other two species are the Massasauga (Sistrurus catenatus), limited primarily to the southeastern grasslands, and the Midget Faded Rattlesnake, found only in the far west-central region.
Rattlesnakes are distinguished from non-venomous snakes by several features. They possess a broad, triangular head that is wider than their neck, and they have vertical, elliptical pupils. A rattle, or at least a single button, at the tip of the tail is the clearest indicator, though they do not always rattle before striking. They also have facial pits, which are heat-sensing organs located between the eye and the nostril.
The Prairie Rattlesnake is typically tan, greenish-gray, or olive green with dark blotches running down its back. The Midget Faded Rattlesnake, a subspecies, is known for its highly toxic venom, which is primarily a neurotoxin, and its smaller size.
Harmless and Common Snake Residents
The vast majority of Colorado’s snakes are non-venomous. Harmless species, such as Garter Snakes, have round pupils and lack the triangular head shape of pit vipers. The Western Terrestrial Garter Snake is common across the state, often seen near water, and identified by a yellow, orange, or white stripe down its back.
The Bullsnake, one of the state’s largest species, is often mistaken for a rattlesnake. It can grow up to six feet and defends itself by vibrating its tail and loudly hissing. The Bullsnake lacks a rattle and is harmless to humans. Similarly, the Western Hognose Snake is recognizable by its upturned snout and may flatten its head and strike in defense, but it poses no risk.
Other common non-venomous snakes include the Yellow-bellied Racer and the Coachwhip, both known for their speed and tendency to dart across open areas during the day. These species are beneficial predators of rodents and insects. Learning to correctly identify these harmless snakes helps reduce unnecessary fear and protects them from being harmed.
Habitats and Seasonal Activity
Snake activity in Colorado is highly seasonal, dependent on external temperatures. They emerge from brumation (a state similar to hibernation) during early spring, typically late March or April, and remain active until mid-fall. During the coldest winter months, they shelter in communal dens, often in rock crevices or abandoned mammal burrows.
Snakes are found in nearly all of Colorado’s environments, from the eastern plains and grasslands to the foothills and canyons. The Prairie Rattlesnake, for example, has been documented at elevations reaching up to 9,500 feet.
In the cooler seasons of spring and fall, snakes are active during the day, basking on sunny rocks, trails, or pavement to raise their body temperature. As summer temperatures rise, they become more nocturnal, hunting during the late afternoon, evening, and overnight hours to avoid the heat.
Coexisting Safely with Colorado Snakes
Minimizing encounters begins with simple avoidance strategies, especially when hiking or working outdoors. Always wear sturdy leather boots and long pants when traversing rocky or grassy terrain, as this protects the feet and ankles. Avoid stepping over logs or rocks without first checking the other side, and never place hands or feet into crevices, holes, or thick brush where a snake might be resting.
For homeowners, reducing the appeal of your yard involves removing hiding spots like woodpiles, rock piles, and dense debris. If you encounter a snake, freeze immediately and slowly back away, ensuring at least five feet of distance. Never attempt to provoke, handle, or kill a snake, as most bites occur during these actions.
Should a bite occur, remain calm and seek professional medical attention immediately by calling the Rocky Mountain Poison and Drug Safety hotline or heading to the nearest hospital. Remove any jewelry or tight-fitting clothing from the affected limb before swelling begins. The bite area should be immobilized and kept at or slightly below the level of the heart.
Actions to Avoid
Do not take the following actions, as they can cause more damage and delay effective treatment:
- Apply a tourniquet.
- Cut the wound to suck out venom.
- Use ice.
- Use heat.