Geographical Range From southeastern Canada, across parts of the eastern and middle United States to Arizona
Habitat Prairies, meadows, marshes, swamps, floodplain forests, woodlands, desert grasslands
Scientific Name Sistrurus catenatus
Conservation Status Not listed by IUCN

Heat-seeking Snakes

Like all pitvipers, Massasauga rattlesnakes have heat-sensitive pits located on each side of the head, between the nostril and eye. These special sensors enable the snakes to hone in on endothermic prey ("warm-blooded" animals that produce heat, like mice and small birds). This heat-seeking ability is especially useful for finding food during the dark of night.

Which Massasauga is Which?

There are three different subspecies, or types, of Massasauga rattlesnakes: the eastern, western, and desert Massasaugas. (We have the first two types at the Saint Louis Zoo.) While they have much in common, the three subspecies all look a little different.

The eastern variety usually has a background color of gray to brownish gray. There's a row of black or dark brown blotches down the middle of the back, and rows of smaller dark spots on each side of the body. The belly is mostly black, with some irregular white or yellowish marks. Though this is the normal color pattern for eastern Massasaugas, some are almost entirely black, except for a few light marks on the throat and chin. Western Massasaugas are more pale; their background color is light gray or tan-gray, and contrasts sharply with the dark brown markings. And the desert-dwelling snakes are even lighter in color; their belly is nearly white and virtually unmarked.

The eastern subspecies is the largest, growing up to 30 inches, or even longer. Somewhat smaller are the western and desert varieties (up to 26 inches and 21 inches, respectively).

All Massasaugas are stout-bodied snakes with triangular-shaped heads. And of course, they all have a rattle on the end of their tail! The rattle is actually a series of interlocking scale segments, which make a buzzing noise when the tail is vibrated. It's great for scaring away enemies!

Food, Flicks, and Fangs

Their heat-seeking ability helps Massasauga rattlesnakes find endothermic prey, such as mice, shrews, and small birds. But these snakes also eat a variety of ectothermic (so-called "cold-blooded") critters, including frogs, lizards, and small snakes.

Although heat sensors don't help Massasaugas find ectothermic prey, these snakes have another secret weapon: their tongue! Like all snakes, Massasaugas flick their forked tongue to sniff out their next meal. Odor particles stick to the tongue, and when the snake brings the tongue back into its mouth, the chemical particles are transferred to the Jacobson's organ. This special sense organ, located on the roof of the snake's mouth, helps interpret airborne smells.

Once Massasaugas have located their prey, they strike, using their fangs to inject it with venom. Their fangs have a special feature: they're moveable! The fangs work like a folding chair, moving forward and down automatically when the snake opens its mouth. When the mouth closes, the fangs fold back against the roof of the mouth. Neat package, huh?

Baby Rattles

When a female Massasauga rattlesnake is ready to mate, she has a special way of announcing it: she sheds her old skin, which releases a special chemical that attracts males. After mating, the female and male go their separate ways.

While she's pregnant, the female feeds very little (or not at all) and survives on fat reserves. This inactivity conserves energy and lessens the probability of encountering predators.

The pregnant female may bask in the sun, which raises the temperature of the eggs and speeds their development. Depending on how much sunbathing she does, the pregnancy can last anywhere from two to four months.

The female gives birth to live young. The snakelings are about nine inches long at birth, and are somewhat paler than the adults. The young ones are born with a single rattle segment (called a button) on their tail. Each time the snakes shed their skin, a new segment is added to the rattle. Older segments become weak and break off.

Migrating Massasaugas

Unlike many other species of snakes, Massasaugas often migrate. In late spring and summer, they live in dry upland areas. In the fall they move to lower, wetter habitats, where they brumate in shelters during the cold winter months. (This means they're in a state similar to hibernation, but with periods of wakefulness.) Massasaugas brumate alone or in small groups, depending in part on the size of the shelter. A large rocky crevice, for instance, can hold a lot more snakes than an abandoned crayfish burrow -- both popular winter dens for Massasaugas.

In the spring, the snakes come out of their dens. They spend some time sunbathing and shedding last year's outer skin, then begin their annual migration to their summer hunting grounds.

Snakes in Danger

Though Massasauga rattlesnakes are not listed as endangered or threatened by IUCN, they are still in trouble in the wild (see Conservation Status). Habitat loss has taken a heavy toll on these reptiles. They're considered endangered in Canada, and they're listed as endangered or threatened in most states in the U.S. where they occur, including Missouri.

The Massasauga rattlesnake is now a candidate for federal listing under the United States Endangered Species Act. If the species is eventually listed as threatened or endangered, it will qualify for legal protection, including habitat protection.

In the meantime, other efforts are underway to help these reptiles. For instance, wetland and prairie restoration projects are helping Massasaugas by bringing back their natural habitat.

The Saint Louis Zoo is doing its part to help eastern Massasaugas. Data collected from field research will enable us to develop a conservation plan for these endangered snakes. Through these efforts, we hope to ensure the future of Massasaugas in Missouri.

Fun Facts

  • The name "Massasauga" comes from a Chippewa Indian word meaning "great river mouth." This probably refers to the wet habitats preferred by the eastern and western subspecies.
  • The venom of the Massasauga rattlesnake is hemolytic, which means it causes the breakdown of red blood cells in its victim. Though the venom is highly toxic, there are very few reports of humans dying from a Massasauga bite.

Class: Reptilia
Order: Squamata
Family: Viperidae