Eastern Massasauga

About the eastern massasauga

The eastern massasauga is a species of rattlesnake found in eastern North America, ranging across southern Ontario, Canada, and eastern portions of the Midwestern United States and Great Lakes region. It's a pit viper and, notably, the only venomous snake found in Ontario. For more than a century, three subspecies of Sistrurus catenatus were recognized, but research published in 2011 elevated two of them to full species — the eastern massasauga (Sistrurus catenatus) and the western massasauga (Sistrurus tergeminus) — leaving the eastern massasauga now considered monotypic, with no subspecies of its own.

Its genus name, Sistrurus, combines Latin and Greek roots for "rattle" and "tail," while the species name catenatus comes from the Latin for "chain," likely a reference to its dorsal blotch pattern. The common name "massasauga" comes from the Ojibwe word for "great river-mouth," probably describing the grasslands around river deltas in Ojibwe country. It also goes by pine rattler, black rattler, swamp rattler, prairie massasauga, and Kirtland's rattlesnake, among other regional names. Adults are modest in size for a rattlesnake, ranging from 60 to 75 cm (24 to 30 in) in total length. The dorsal pattern is gray or tan with a row of large, rounded brown or black blotches down the center of the back and three smaller rows of alternating spots along each side; some individuals are solid black. Young massasaugas show the same pattern but in paler tones. Both young and adults have heat-sensing pits on either side of a relatively small head, keeled dorsal scales, and a single anal scale.

Behavior and diet

The eastern massasauga's diet includes a range of small vertebrates — rodents such as voles, white-footed mice, jumping mice, and shrews make up much of the adult diet, while juveniles more often take reptiles, especially lizards in western populations and snakes in eastern ones. Frogs are also an important food source in some populations; one researcher found frogs made up the main portion of the diet in Michigan, and this species is reported to eat frogs more often than any other rattlesnake, even though frogs aren't typically a major part of its diet range-wide. Birds, bird eggs, centipedes, and other insects round out the menu.

Reproduction follows an ovoviviparous pattern typical of rattlesnakes. Females reach reproductive size at a minimum of 32.5 cm (12.8 in), usually by their third or fourth year, and most don't reproduce every year — a biennial cycle is typical. Births, or parturition, generally happen in August or September. Litter sizes of 5 to 14 have been recorded in Illinois populations, and 6 to 19 in Wisconsin, where a few females were noted to breed annually. Newborns measure 18.8-24.4 cm (7.4-9.6 in) snout to vent, and mother and young stay together for only a few days, until the neonates shed their skin for the first time.

The species is generally shy and avoids humans when possible. It's most often found near its overwintering site, or hibernaculum, in spring and fall, frequently occupying abandoned crayfish burrows, and it may move to drier ground in summer, particularly among pregnant females.

Range and habitat

The eastern massasauga is endemic to North America, occurring in the Great Lakes region and eastern portions of the Midwestern United States. Historically its range covered southern Ontario from the North Channel eastward across Georgian Bay and Lake Huron to the Niagara Peninsula, and in the U.S. it extended through most of lower Michigan, the Finger Lakes and Central New York, northwest Pennsylvania, northern Ohio and Indiana, much of Illinois, southern Wisconsin, eastern Iowa, and marginal parts of eastern Missouri and Minnesota. The species is most often found near wetlands — swamps, marshes, bogs, fens with sedges, shrubby peatlands, wet meadows, and floodplains — along with wetland areas within meadows, prairies, and coniferous forests.

Much of that historical range has since fragmented into smaller, isolated populations. Illinois, once described as having the species common across the northern two-thirds of the state, now has only six to eight relict populations left in five or six counties, and Pennsylvania went from 19 known populations in six counties to just six populations in three counties by 1977. Draining of wetlands, agriculture, highway construction, and urban development are the major causes of the decline.

Conservation status

The eastern massasauga was listed as a species of Least Concern on the IUCN Red List in 2007, though that assessment is flagged as needing an update and its population trend was listed as unknown at the time. Despite that global rating, it's been listed as a federally threatened species under the U.S. Endangered Species Act since 2016 and remains a candidate for full endangered status. Individual states list it as endangered in Illinois, Indiana, Iowa, Minnesota, Missouri (where it's also considered extirpated), New York, Ohio, Pennsylvania, and Wisconsin; Michigan, the only state where it isn't listed as endangered, classifies it as a species of special concern. In Canada, it's listed as threatened under Ontario's Endangered Species Act and the federal Species at Risk Act, and it now survives only near the eastern shore of Georgian Bay, the Bruce Peninsula, the North Shore of Lake Huron, Wainfleet Bog, and Ojibway Prairie.

The species is also one of several rattlesnakes threatened by snake fungal disease, which affects the skin. Its venom is cytotoxic, destroying tissue and disrupting blood clotting in prey, but the species is shy around humans, and most recorded bites in Ontario have followed someone deliberately handling or accidentally stepping on a snake — only two fatalities have ever been recorded there, both involving improper treatment.