Yellowstone National Park has five confirmed snake species: bullsnake, prairie rattlesnake, rubber boa, common gartersnake, and terrestrial gartersnake. The National Park Service (NPS) lists six confirmed reptiles in all; the sixth is the sagebrush lizard, not a snake.
The prairie rattlesnake is the park’s only dangerously venomous snake. The other species still deserve distance and respect, especially because bullsnakes can be mistaken for rattlesnakes and snakes are easy to stress or injure when handled.
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How many snake species live in Yellowstone?
The NPS inventory confirms five snake species in Yellowstone National Park. They occupy very different settings, from warm, dry country along the lower Yellowstone River to streams, meadows, and wetlands across the park. The NPS says reptiles are not well studied in Yellowstone; researchers began a formal reptile and amphibian inventory in 2000. The inventory confirms presence, but it does not provide reliable visitor encounter odds, population estimates, or a complete month-by-month sighting calendar.
“Snake” and “reptile” are not interchangeable here. Yellowstone’s six confirmed reptiles comprise the five snakes below plus the sagebrush lizard.
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| Species | Stated size | Appearance described by NPS | Where it is reported or usually found | Venom risk |
|---|---|---|---|---|
| Bullsnake | Not stated in the cited NPS inventory | NPS notes that its appearance and behavior often lead people to mistake it for a rattlesnake | Specific park distribution not stated in the cited inventory | The prairie rattlesnake is the only dangerously venomous Yellowstone snake identified by NPS |
| Prairie rattlesnake (Crotalus viridis) | Can exceed 48 inches | Greenish gray, olive, greenish brown, light brown, or yellowish; dark-brown dorsal blotches bordered in white | Lower Yellowstone River area, including Reese Creek, Stephens Creek, and Rattlesnake Butte | Only dangerously venomous snake in the park |
| Rubber boa (Charina bottae) | Up to 28 inches | Brown or greenish-brown back, lemon-yellow belly, small smooth scales | Rocky places near streams or rivers with nearby shrubs or trees; recent sightings in Bechler and Gibbon Meadows | Not identified by NPS as dangerously venomous |
| Common gartersnake (Thamnophis sirtalis) | Up to 34 inches | Nearly black or dark green base, three bright lengthwise stripes, pale yellow or bluish-gray underside, and irregular red side spots | Permanent surface water; NPS reports the Falls River drainage in Bechler and an area three miles south of the south entrance along the Snake River | Not identified by NPS as dangerously venomous |
| Terrestrial gartersnake (Thamnophis elegans) | 6 to 30 inches | Brown, brownish green, or gray with three light stripes: one on the back and one on each side | Near water throughout Yellowstone; NPS calls it the park’s most common reptile | Not identified by NPS as dangerously venomous |
The five Yellowstone snakes, one by one
Bullsnake
Bullsnakes are one of the five confirmed Yellowstone snake species. The most important visitor-facing fact in the NPS inventory is the identification problem: bullsnakes are often mistaken for rattlesnakes because of their appearance and behavior. A snake that looks or acts like a rattlesnake from a visitor’s viewpoint should therefore be treated as an animal that needs space, not as an identification challenge.
The cited NPS inventory does not supply a Yellowstone-specific bullsnake length, color chart, habitat map, or encounter frequency. That absence is useful information: do not rely on a generic field-guide measurement or a single visual cue to identify one on a trail. Stop, give the snake room, and let it move away. If you cannot identify it confidently without approaching, you do not have enough information to approach.
Prairie rattlesnake (Crotalus viridis)
Prairie rattlesnakes are the only dangerously venomous snakes in Yellowstone. NPS says they can exceed 48 inches (4 feet) and describes color ranging from greenish gray or olive green to greenish brown, light brown, or yellowish. Dark-brown blotches bordered in white run along the back.
The park profile places them in the lower Yellowstone River area, including Reese Creek, Stephens Creek, and Rattlesnake Butte. Those locations are warmer and drier than much of the park, so a sighting there is consistent with the habitat described by NPS rather than evidence that rattlesnakes are equally common everywhere in Yellowstone.
NPS describes the species as usually defensive rather than aggressive. That wording does not make close approach safe. A defensive snake may protect itself when cornered, stepped near, touched, or blocked from retreat. The park profile records only two known snake bites during Yellowstone’s history. That is an NPS historical count, not a current probability estimate and not a promise that a visitor cannot be bitten.
Rubber boa (Charina bottae)
Rubber boas are infrequently encountered, probably in part because they are nocturnal and spend time underground. They can reach 28 inches. NPS describes a brown or greenish-brown back, lemon-yellow belly, and small smooth scales. Individuals may be partly buried beneath leaves and soil or inside rodent burrows, making a daytime sighting unusual even where the habitat is suitable.
The usual setting is rocky ground near a stream or river with shrubs or trees close by. NPS lists recent sightings in Bechler and Gibbon Meadows. “Recent” refers to the sightings noted in the NPS profile; it is not a claim that those areas offer a predictable viewing opportunity. Searching under rocks, probing burrows, or lifting logs can injure a boa and put a person within striking distance of any snake hidden there.
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Common gartersnake (Thamnophis sirtalis)
The common gartersnake is a medium-sized snake that NPS describes as reaching 34 inches. Its base color may be nearly black or dark green, with three bright lengthwise stripes. The underside is pale yellow or bluish gray, and irregular red side spots are a distinguishing regional feature in the NPS description.
This snake is closely associated with permanent surface water. NPS reports observations in the Falls River drainage in Bechler and three miles south of Yellowstone’s south entrance along the Snake River. The second location is outside the national park boundary, so the NPS account should be read as a report of Yellowstone-area observations, not as proof that every listed site lies inside the park. The profile does not establish how often visitors will see common gartersnakes at those places.
Terrestrial gartersnake (Thamnophis elegans)
The terrestrial gartersnake is Yellowstone’s most common reptile, according to NPS. It measures 6 to 30 inches and is typically brown, brownish green, or gray with three light stripes: one down the back and one along each side. It is usually found near water throughout the park, making streams, ponds, wet meadows, and similar edges more plausible places to notice one than dry open ground.
NPS documents a broad diet: small mammals, fish, frogs, tadpoles, salamanders, earthworms, slugs, snails, and leeches. Seeing one near water does not mean it is hunting a particular prey item; the list simply shows how flexible this species’ feeding ecology can be. Its abundance also does not justify handling or moving snakes encountered on paths.
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Yes. The prairie rattlesnake is a confirmed Yellowstone species and the park’s only dangerously venomous snake. NPS associates it especially with the lower Yellowstone River area, including Reese Creek, Stephens Creek, and Rattlesnake Butte.
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Do not use a rattle, head shape, color, or any other single feature as a do-it-yourself safety test at close range. The NPS specifically warns that bullsnakes are often mistaken for rattlesnakes based on appearance and behavior. From a safe distance, the correct response is the same either way: stop, back away, and leave a clear route for the snake.
Are Yellowstone snakes poisonous?
For the visitor’s practical question—“Could a snake’s bite inject venom?”—the NPS identifies only the prairie rattlesnake as dangerously venomous in Yellowstone. “Poisonous” generally refers to harm caused by eating or absorbing a toxin, while “venomous” refers to toxin delivered by a bite or sting. Regardless of terminology, never pick up a snake to determine which category it belongs to.
The other four species are not identified by NPS as dangerously venomous, but that is not an invitation to touch them. Handling can injure a snake, provoke a defensive bite, and expose both the animal and the person to unnecessary risk.
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The available NPS profiles support habitat and distribution descriptions, not visitor sighting probabilities. Terrestrial gartersnakes may occur near water throughout the park. Common gartersnakes are tied to permanent surface water, with NPS reports from Bechler’s Falls River drainage and the Snake River south of the south entrance. Rubber boas favor rocky stream or river margins with nearby vegetation and are infrequently seen because they are nocturnal and burrowing. Prairie rattlesnakes are associated with the warmer, drier lower Yellowstone River area. The cited inventory does not provide a complete seasonal calendar for any species.
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Snakes may be concealed under soil, leaves, rocks, or vegetation even in suitable habitat. A quiet trail with no sightings does not indicate that snakes are absent, and a sighting does not indicate that a trail has unusually high snake density.
How to watch a Yellowstone snake safely
- Stop moving toward it. Freeze or step back rather than walking over, around, or beside the snake.
- Keep the NPS wildlife distance. NPS’s general rule is to remain at least 25 yards from wildlife other than bears, wolves, and cougars. The rule is not snake-specific, but it is the park’s stated minimum for other wildlife and provides a conservative boundary.
- Give it an escape route. Do not surround it, block the trail, throw objects, poke it, or try to make it move for a photograph.
- Keep people and pets back. Children should stay beside an adult, and a dog should be leashed and moved away without pulling it toward the snake.
- Leave the animal where it is. Do not capture, relocate, or transport a wild snake, even if it appears injured or is on a road.
- Report a conflict. If a snake is trapped in a building, vehicle, or crowded facility, notify a ranger rather than attempting removal.
For an emergency, call 911 or notify a ranger. The NPS wildlife guidance is not a snake-bite first-aid protocol; a suspected venomous bite requires urgent medical help and should not be managed by experimenting with cuts, suction, or tourniquets.
How to identify a snake without taking risks
Start with distance, location, and behavior rather than trying to inspect fine details. Note the general habitat, approximate length, broad color pattern, and whether the snake is moving toward cover. Use binoculars or a camera’s optical zoom if you already have one; do not move closer to improve a photograph.
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For a possible prairie rattlesnake, the lower Yellowstone River setting and the profile’s greenish, brown, or yellowish colors with dark blotches bordered in white may be consistent, but they are not a license to approach. For a possible rubber boa, nocturnal activity, a smooth-scaled brown or greenish-brown back, and a lemon-yellow belly fit the NPS description, yet a partly buried snake should be left undisturbed. Terrestrial and common gartersnakes both have stripes, so water setting and the precise pattern described by NPS can be useful only from a safe distance.
Bullsnake identification is particularly unsuitable for close inspection because NPS documents frequent confusion with rattlesnakes. If the identification matters for a safety decision, assume you have not identified it and increase your distance.
What the official information does—and does not—tell you
The NPS inventory confirms species presence and supplies profile-level descriptions, but reptiles have received less study than amphibians in Yellowstone. The published material does not establish a park-wide population count, a probability that a particular trail user will see a snake, or a comprehensive seasonal sighting schedule. Treat location statements as documented habitat or observation areas, not guarantees.
NPS reptile profiles used for these descriptions were published or updated in 2025 and 2026. Park boundaries, access, closures, and wildlife instructions can change, so check the current National Park Service reptile and safety pages before a trip. A broad regional field guide such as Stebbins’ A Field Guide to Western Reptiles and Amphibians, 3rd edition, can help with study after you understand and follow park-distance rules; it is not required safety equipment and is not Yellowstone-specific.
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