About Snakes

Colorado Snakes by the Numbers

FIELD GUIDE

Colorado's Common Snakes

Four snakes you are most likely to run into around Castle Rock, what to look for, and which ones to leave well alone. Click a square to jump to a species or scroll through them all below.

Bullsnake Pituophis catenifer sayi

NON-VENOMOUSTHREAT 2/10

One of the largest snakes in Colorado and the one most often mistaken for a rattlesnake. A powerful, non-venomous constrictor that does far more good than harm, and a common sight on Front Range properties. Also called a gopher snake.

Identification

• Large and heavy bodied, often four to six feet, sometimes up to eight
• Yellow, cream, or tan with dark brown or black blotches down the back
• Pointed snout and a relatively small head, not a broad triangle
• No rattle, though it vibrates its pointed tail to fake one
• Round pupils, unlike a rattlesnake's vertical slits

Habitat

• Open grassland, fields, and brushy property edges
• Rodent burrows, which it follows and takes over
• Rock piles, woodpiles, and foundation gaps near the house
• Gardens and outbuildings where mice and rats are active

Behavior

Bullsnakes are excellent rodent hunters, killing by constriction, and a single one keeps a remarkable number of mice and rats in check. Threatened, it puts on a dramatic show: hissing loudly, flattening its head, coiling, and buzzing its tail to imitate a rattlesnake. It is all bluff. Bullsnakes are also known to kill and eat rattlesnakes, so one on the property can mean fewer venomous snakes.

Danger & What to Do

Non-venomous and not a medical threat. A cornered bullsnake can give a defensive bite that might bleed a little, but there is no venom involved. Because they look and act so much like rattlesnakes, the real danger is panic and misidentification. Give one space and let it move on, or have it relocated. Killing bullsnakes is counterproductive, since they suppress both rodents and rattlesnakes.

Garter Snake Thamnophis

NON-VENOMOUSTHREAT 1/10

The snake Coloradans see most often: small, harmless, and striped, turning up in gardens, near water, and under cover around the yard. Protected under Colorado law and one of the most beneficial snakes you can have around.

Identification

• Slender, typically eighteen to twenty-six inches
• Three light stripes down a darker body, usually yellow, green, or tan
• A slightly rough, non-glossy look from ridged scales
• Small head only a little wider than the neck
• No rattle, round pupils

Habitat

• Damp areas near ponds, streams, ditches, and watered beds
• Tall grass, gardens, and ground cover
• Under rocks, logs, boards, and debris
• Shared underground dens in winter, where many gather to hibernate

Behavior

Garter snakes are active by day and hunt earthworms, slugs, insects, small fish, and rodents. They flee readily and are rarely aggressive. Grabbed, a garter may release a harmless, foul-smelling musk and occasionally a tiny bite. In fall they congregate at communal dens to overwinter, which is the source of many nest of snakes sightings.

Danger & What to Do

Effectively harmless. Garter snakes produce a very mild saliva toxin that helps subdue prey like worms, but it has no meaningful effect on people beyond, very rarely, slight itching at a bite. They are protected under Colorado law and cannot legally be killed. Leave them be, since they quietly control garden pests, or have one relocated if it turns up somewhere unwelcome.

Western Rattlesnake Crotalus viridis

VENOMOUSTHREAT 9/10

Colorado's most widespread venomous snake and the one to take seriously. A pit viper whose bite is a genuine medical emergency. Most encounters happen on warm-season hikes and on properties backing up to open space.

Identification

• Heavy, thick body, usually three to four feet
• Tan, brown, or greenish-gray with dark, light-edged blotches
• Broad triangular head clearly wider than the neck
• A segmented rattle at the end of the tail
• Vertical, cat-like pupils and heat-sensing pits by the nostrils

Habitat

• Open prairie, grassland, and rocky hillsides
• Property edges bordering fields or open space
• Rock outcrops, ledges, and south-facing slopes for basking
• Rodent burrows and shaded cover during the heat of the day

Behavior

Prairie rattlesnakes are most active spring through fall and hunt rodents with their heat-sensing pits. They would rather avoid people and usually rattle a warning, but a startled or cornered snake will strike with little notice. They bear live young, a dozen or more, in late summer, and retreat to communal dens in the cold months.

Danger & What to Do

Venomous and dangerous. The venom damages tissue and affects blood and clotting, and a bite brings intense pain and swelling and can be life-threatening without prompt care. Dogs are at especially high risk because they investigate with their nose. If you meet one: stop, keep well back, keep pets and children away, and give it a clear path to leave. Never try to handle or kill it, since most bites happen during those attempts. Call a professional to relocate one from an occupied property, and treat any bite as an emergency.

Midget Faded Rattlesnake Crotalus oreganus concolor

VENOMOUSTHREAT 8/10

A small, pale rattlesnake of western Colorado's canyon country. Its modest size is deceptive: drop for drop, its venom is among the most potent of any North American rattlesnake.

Identification

• Small for a rattlesnake, usually under two feet
• Pale, washed-out cream, tan, yellowish, or light gray with faint blotches
• Broad triangular head and a small rattle
• Vertical pupils and heat-sensing pits

Habitat

• Rocky canyons, ledges, and outcrops, mainly in western Colorado
• Crevices and talus where it shelters and dens
• Sun-warmed rock in cool hours, shade during heat

Behavior

Secretive and often active at dusk and after dark, especially in hot weather. It feeds on lizards and small rodents. Like other rattlesnakes it prefers to avoid confrontation and will rattle if cornered, but its small size and pale color make it easy to overlook.

Danger & What to Do

Venomous, with disproportionately potent venom for its size, so a bite is a serious medical emergency despite the small frame. Treat it exactly as you would any rattlesnake: keep your distance, keep pets and people back, do not attempt to handle or kill it, and call a professional to relocate one found on an occupied property. Seek immediate medical care for any bite.

SNAKE NESTS

What a Snake Nest Actually Is

The phrase snake nest conjures a writhing ball of snakes, but that is not how snakes live. Snakes are solitary. They do not form colonies, and they do not build nests the way birds do. What people call a snake nest is usually one of a few different things, and most of them are nothing to fear.

When a female is ready to lay, she finds a sheltered spot, an existing burrow or a gap under rock or debris, and leaves the eggs there, usually unattended. A cluster of snakes seen together in spring is more often a mating event, and a group sharing a spot over winter is a hibernaculum, a shared den. Garter snakes in particular gather to hibernate, then scatter as it warms.

Common Snake Questions

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