Desert Massasauga

Overview

The desert massasauga is a small, secretive rattlesnake of Colorado’s southeastern plains. It is gray to light brown, with 37 to 40 darker brown saddles or blotches outlined in black down its back. A dark stripe runs from the eye to the angle of the jaw, and a lyre-shaped set of stripes runs from the top of the head to the first blotch. The rattle is usually black at the base; in newborns its tip is yellow.

CPW calls it the Desert Massasauga, Sistrurus tergeminus, and lists it as a State Special Concern species and a Tier 2 Species of Greatest Conservation Need in its 2025 State Wildlife Action Plan. NatureServe ranks the desert subspecies, S. t. edwardsii, G3T3 (vulnerable) across its range and S2, imperiled, in Colorado. The U.S. Fish and Wildlife Service’s ECOS database still files it under the older name Sistrurus catenatus edwardsii.

Natural History

Adults average about 15 inches long and reach about 23 inches at most, small for a rattlesnake. Desert massasaugas eat lizards, small mammals and centipedes.

They are mostly nocturnal. In Colorado they hibernate from October to mid-April, often in rodent burrows, which they also use as birthing sites. Some travel up to about 1.2 miles between winter sites and summer range. Females give birth in summer to 4 to 8 young and may not breed every year. Most adults found in the field were estimated to be 4 years old or younger, though massasaugas have lived more than 14 years in captivity.

Habitat in Colorado

Colorado studies found the snake mainly in shortgrass prairie with sand sage, buffalograss and blue grama, below about 5,000 feet. It is most abundant in the moister parts of that prairie. Grass gives it cover for catching prey and avoiding predators.

The southeastern Colorado population is especially isolated from the rest of the subspecies’ range, which runs through Texas, southern New Mexico, southeastern Arizona and northern Mexico.

Primary Threats

USFWS based its 2012 finding mainly on two threats: habitat loss and degradation, and vehicle strikes.

• Plowed prairie. When native shortgrass prairie becomes cropland, massasauga habitat is lost outright; the snakes can’t find shelter, prey or hibernation sites in cultivated fields. Researchers named grassland conversion as a concern in southeastern Colorado. See habitat loss.
• Overgrazing. Properly managed grazing can be compatible with the snake, but overgrazing that badly degrades shortgrass prairie leaves it unable to live there.
• Roads. Massasaugas cross roads during spring and fall movements and bask on warm pavement in the evening. During one week in May 2005, a Colorado landowner collected 15 dead desert massasaugas along a 1-mile stretch of remote gravel road, and some were run over on purpose. See roads and vehicles.

Federal Status

On October 28, 2010, WildEarth Guardians petitioned USFWS to list the desert massasauga as endangered or threatened, or alternatively to list a distinct population segment in Colorado, Kansas and Oklahoma. On August 9, 2012, USFWS published a 90-day finding that the petition presented substantial information that listing may be warranted, and opened a status review (77 FR 47583). A substantial 90-day finding is not a decision to list. We found no 12-month finding on the petition, and ECOS lists the subspecies as not listed.

Conservation and Research

Rangewide, population sizes and trends are largely unknown because so little data has been collected, USFWS wrote in 2012. Long-term research in southeastern Colorado found some local populations “reasonably robust and stable” where habitat was intact.

That gap is not unique to the massasauga. In 2022, CPW’s species conservation supervisor, David Klute, told the Parks and Wildlife Commission that the agency had done little to directly understand and conserve reptiles and that much of that work was still ahead, The Gazette reported.

What You Can Do

• Leave it be. Under CPW’s 2026 herpetofauna rules (Chapter W-7, #705), people may briefly catch most wild reptiles to identify or photograph them, but not desert massasaugas or prairie rattlesnakes.
• Drive slowly on plains roads at night, especially in spring and fall, and don’t swerve to hit snakes.
• Keep native prairie intact, and graze it in a way that leaves grass cover.
• Report sightings of rare reptiles; see Report a Sighting.
• Explore related species. Read the prairie rattlesnake and long-nosed leopard lizard profiles.