● Venomous · Native to the United States

Eastern massasauga

Sistrurus catenatus (Rafinesque, 1818)

Also called eastern massasauga rattlesnake, swamp rattler
Data updated October 2026

Eastern massasauga coiled in a sedge meadow, showing dark brown blotches on a gray body
Fig. 1 — Adult in a sedge meadow. Dark, light-edged blotches run down a gray to gray-brown back.
Close view of an eastern massasauga's head with a dark stripe behind the eye and a vertical pupil
Fig. 2 — A dark stripe runs from each eye down the side of the head.

At a glance

A small, thick-bodied rattlesnake of Great Lakes wetlands, federally listed as threatened since 2016. It is shy, relies on camouflage and bites rarely. Every bite still needs emergency care.

01

Identification

The eastern massasauga is a small, stout rattlesnake with a gray, gray-brown or light brown body. Large chocolate-brown to black blotches, often edged in pale scales, run down the back, with smaller blotches on the sides. The belly is dark gray or black, and the tail carries dark rings ending in a blunt rattle. Some individuals are almost completely black. Like other pit vipers it has a triangular head, vertical pupils and a heat-sensing pit between eye and nostril. Newborns are lighter in color and have only a button, so they cannot rattle.

  1. 01Rattle on a ringed tail. A segmented rattle at the tip of a dark-ringed tail. No other snake in its range has one.
  2. 02Nine large head plates. Big symmetrical scales on top of the head, plus a dark stripe from each eye down the side of the head.
  3. 03Dark belly. The underside is dark gray to black, not cream or checkered.

Commonly confused with

02

Size

01 ft2 ft3 ft4 ft Typical adult · about 24 in (61 cm)

Adults measure about 18 to 39.5 inches (45–100 cm) and average about 2 feet (60 cm). Newborns are 7 to 10 inches (18–25 cm) long.

03

Range & habitat

Eastern massasauga basking at the edge of a fen with sedges and shrubs
Fig. 3 — Open, sunny wetlands such as fens, sedge meadows and wet prairies are core habitat.

Eastern massasaugas live around the Great Lakes, from southern Ontario and western New York through Michigan and southern Wisconsin, south to Illinois, Indiana, Ohio and northwestern Pennsylvania, with small numbers in eastern Iowa. Michigan and Ontario are the remaining strongholds. The species is likely gone from Minnesota and possibly from eastern Missouri. Massasaugas found in Texas and Oklahoma belong to a separate species, the western massasauga.

They use shallow wetlands and the uplands next to them. Wet prairies, marshes, fens, bogs, sedge meadows, peatlands, shrub thickets and swampy forest provide shelter and winter sites. For part of the year they move into nearby prairies, old fields, savannas and open woods to bask, hunt and give birth. Good sites mix sunny openings with shade and have a water table close to the surface.

04

Diet & predators

Small mammals are the main food, especially voles, mice and shrews. Massasaugas also eat other snakes and occasionally birds, frogs and lizards. Young snakes feed mostly on small mammals and snakes. They depend on camouflage, waiting in cover for prey to come close.

Feeds on

  • Voles and mice
  • Shrews
  • Other snakes
  • Frogs, birds and lizards (occasionally)

Preyed on by

  • Hawks and wild turkeys
  • Herons and other large wading birds
  • Raccoons, skunks and weasels
  • Foxes and coyotes
Small wild rodent in grass
Prey — voles and mice.
Red-tailed hawk perched over a meadow
Predator — hawks.

05

Behavior & seasons

Eastern massasaugas are shy and generally unaggressive. When threatened they usually stay still and trust their camouflage. They rattle when alarmed but may strike without warning if surprised, so bites mostly happen when someone steps on or grabs one. They swim well. Males roam farther than females and may wrestle over mates without hurting each other.

In Michigan they are active from mid-March or April to October or early November. In spring and fall they are most active around midday; in summer they shift to mornings, evenings and sometimes nights. Winter is spent in crayfish or small mammal burrows, old stumps and root systems near wetland edges, often partly in groundwater that does not freeze. Unlike many rattlesnakes, they do not gather in large dens; they hibernate alone or in groups of a few, and return to the same sites year after year.

06

Reproduction

Eastern massasaugas give birth to live young, which emerge from thin membranes at birth. Mating can happen in spring, summer or fall. Pregnancy lasts about 100 days, and litters of 8 to 20 young are born from late July to early October, mostly in August. Females mature at three or four years old and breed every year or every other year, depending on the population. Many return to the same area to give birth in later years.

07

Conservation

The U.S. Fish and Wildlife Service listed the eastern massasauga as threatened under the Endangered Species Act in 2016, after it was recognized as a separate species from the western massasauga in 2011. Loss of wetland habitat is the main cause of decline, along with drainage, development, roads, fragmentation, fire suppression that lets open wetlands grow over, and killing by people. About 40 percent of the counties where it was once recorded no longer have it, and the populations that remain are small and isolated, especially at the edges of the range. Michigan lists it as a species of special concern, and taking one from the wild there requires a permit. Most other states and provinces in its range list it as endangered or threatened.

Browse endangered and threatened US reptiles →

08 — Bite safety

If someone is bitten

Eastern massasauga bites are a medical emergency. Every bite needs medical care. Call 911 or go to the nearest emergency department. For guidance, call Poison Control at 1-800-222-1222. If a pet is bitten, take it to a veterinarian right away.

This page does not give first-aid or treatment instructions. Read our safety disclaimer.

Keep reading

Sources

Data updated October 2026 · How we build these pages