Prairie Rattlesnake – Venomous
The prairie rattlesnake is the only venomous snake in the park, but odds are slim that you’ll run into this wiggling Yellowstone inhabitant. It can range in color from greenish-gray to olive, greenish brown or light brown to yellowish with dark brown splotches bordered in white and can reach more than 48 inches in length. The snakes are most often spotted in the lower Yellowstone River areas, like Reese Creek, Stephens Creek, and Rattlesnake Butte. These regions are drier and warmer, conditions more suitable for the rattlesnake. While it can’t hurt to be on the lookout for these slitherers, the National Park Service has only recorded two rattlesnake bites in Yellowstone’s history. Generally the snakes are defensive rather than aggressive, but if you hear a rattling while on a hike, immediately and slowly move in the opposite direction of the sound.
Bullsnake – Not venomous
The bullsnake is a subspecies of the gopher snake, but it tends to act more like a rattler when it’s startled. If it feels as if it’s in danger, the snake will coil up, hiss and move its tail against the ground, producing a rattling sound. Unlike the rattlesnake however, bullsnakes are not poisonous. These snakes eat small rodents, can grow to 72 inches and tend to be yellowish with black, brown or reddish-brown circles along its back with a dark band going from the lower jaw up through the eye to the top of its head. You’re most likely to run into a bullsnake at lower elevations in the dry, warm, open areas around Mammoth.
Rubber Boa – Not venomous
Named for their rubbery appearance gained by its collection of small, smooth scales, the rubber boa is rarely seen in Yellowstone, likely because of its nocturnal habits. These rodent-eating reptiles spend most of their time partially buried under fallen leaves and dirt or hunting prey in rodent holes. The rubber boa can reach up to 24 inches long and has a gray or greenish-brown back and yellow belly. They’ve been spotted recently in the Bechler region and Gibbon Meadows.
Valley Garter Snake – Not venomous
A subspecies of the common garter snake, the valley garter snake stretches up to 34 inches long and is typically found near permanent surface water in the Bechler region’s Falls River drainage. They have a pale yellow or bluish-gray belly and three bright longitudinal stripes running all along the body interrupting the blackish background color. Red spots in irregular patterns dot the snake’s sides. The valley garter snake tends to be active during the day and generally eats toads, chorus frogs, fish remains and earthworms.
Wandering Garter Snake – Not venomous
The wandering garter snake is the most common reptile in the park. These harmless snakes live in coniferous regions, typically near water, all throughout the park eating rodents, fish, frogs, tadpoles, salamanders, earthworms, slugs, snails and leeches. Generally black with three bright stripes on its back and sides, it may also have red or black spots along its sides.