Michigan Society of Herpetologists
EASTERN MASSASAUGA RATTLESNAKE
Sistrurus catenatus catenatus
Michigan's Only Venomous Snake
Description: This is a medium-sized, thick-bodied snake with a segmented rattle on the tail tip, an opening ("pit") between eye and nostril, and elliptical ("catlike") pupils. A row of 21 to 40 large, dark brown, black-edged blotches runs down the back; these are sometimes outlined with thin white or yellowish margins. Two or three additional rows of dark spots alternate along the sides, the lowest of these contacting the ventral, (belly) scutes, and there are alternating dark and light bands around the tail. The background color is gray, gray-brown, or brown. The head is widened toward the back and distinct from the neck. A dark stripe extends back from the eyer bordered below by a white stripe, and there are two dark stripes on the back of the head extending onto the neck. The belly is usually black with gray, yellowish, or white mottling. Occasional indiv1duals are entirely black (melanistic) except for light markings on the chin, throat, and "lip." The subcaudal (undertail) scutes are undivided except for a few near the rattle. There are usually 25 (19-27) scale rows at midbody; the scales are keeled and the anal plate is single. Total adult length: 47 to 100.3 cm (18.5 to 39.5 in). Males have relatively longer tails than females. Tail length is usually equal to or greater than 10 percent of the total length in males, but less than 10 percent of total length in females.
Newborn Eastern Massasaugas range in length from 18 to 25.6 cm (7 to l0 in). They are similar to adults, but with a lighter background color; the tail is yellowish below, and the rattle is represented by a single "button." The spotted pattern is present even in young Massasaugas that will be melanistic as adults. Fangs and venom glands (and the ability to use them) are present at birth.Back to Top
Confusing Species: All nonvenomous snakes in the region have round (not elliptical) eye pupils In daylight, and do not have a "pit" between eye and nostril or rattles on the tail-though many species will vibrate the tail tip when alarmed. Timber Rattlesnakes have many small scales on the head between the eyes, and the tail is usually all-black; Massasaugas have enlarged head scales and banded tails.
Distribution and Status: This snake ranges from western New York, western Pennsylvania, and southern Ontario west to eastern Iowa and eastern Missouri. Western subspecies extend the species' range from western Missouri and southeast Nebraska south to the Texas Gulf Coast and west to Arizona, with isolated colonies in east-central Colorado and northern Mexico.
Eastern Massasaugas were once common across much of the lower Great Lakes basin but are now restricted to scattered and often isolated colonies. Only two populations are known to remain in the Lake Ontario drainage of New York. They are locally common in southern Ontario (e.g., on some Georgian Bay islands and the Bruce Peninsula, and scattered shoreline sites along Lake Erie and Lake St. Clair), and are uncommon and local, but widely distributed, across Michigan's Lower Peninsula; they have not been reported on the Upper Peninsula mainland but are present on Bois Blanc Island (which is part of Mackinac County in the Upper Peninsula). They occur very locally across northern Ohio and northern Indiana, including the Indiana Dunes area but are nearly (if not completely) extirpated in the Lake Michigan drainage of Illinois and Wisconsin. The Eastern Massasauga is considered endangered, threatened, or a "special concern" species throughout its range.Back to Top
Habitat and Ecology: Eastern Massasaugas are usually associated with damp lowlands, including river bottom woodlands, shrub swamps, bogs and fens, marsh borders, sedge meadows, and moist prairie. The preferred habitat is reflected in the name massasauga, which means "great river mouth" in the Chippewa language. Such lowland habitats are occupied from early fall into late spring (typically from late September or October into June). In early summer many Massasaugas move into adjacent well-drained uplands to spend the warmer months foraging in shrubby fields and grasslands, including pastures and hay fields, (Farmers often report seeing these snakes-and occasionally baling them up-while harvesting forage crops in summer.)
These snakes usually overwinter singly in crayfish or mammal burrows, often close to the groundwater level, and emerge in April as water levels rise. Although they swim well when neccessary, they spend much time in spring basking on whatever high ground is available, such as sedge and grass clumps, muskrat and beaver lodges, or the edges of dikes and other embankments. At this time, and in fall, Massasaugas are most active during daylight hours. Later in the heat of summer their periods of activity shift to the early morning, late evening, and night. The total area utilized by a Massasauga during a year can be quite small, frequently encompassing less than l or 2 hectares (2.5 to 5 acres).
Small mammals make up the bulk of this snake's diet, with voles (Microtus) being the favorite prey, followed in frequency by deer mice (Peromyscus), jumping mice (Zapus), and shrews, Nonmammalianprey taken on occasion includes other snakes, frogs, birds, bird eggs, and insects. Young Massasaugas are particularly inclined to eat smaller snakes and may lure prey animals (especially frogs) within range by twitching their yellowish tail tips. Massasaugas usually strike and release adult rodents and shrews, then wait for the venom to immobilize the animal before swallowing it; nonthreatening prey (e.g., frogs, babymice) may,be simply seized and swallowed without envenomation.
Large snakes such as Racers are known to eat Massasaugas, and it is likely that some birds (herons, hawks) and mammals (raccoons, foxes) are able to kill them at times. Deer are said to trample these (and other) snakes, and domestic hogs, well known for their tendency to kill snakes, have been used by people to eliminate rattlesnakes from certain areas. (According to local legend, Belle Isle, now a park in the Detroit River in southeast Michigan, was cleared of a once-abundant rattlesnake fauna, in the eighteenth century using this method.) There is little doubt that humans are this snake's most important enemy.
The Massasauga's first line of defense is to avoid being seen, and its earth-toned color pattern offers excellent camouflage. Most will "freeze" when approached and frequently remain undetected by people passing close by. Should a potential enemy come too close or even touch a Massasauga, it may try to flee into thick vegetation or choose to stand its ground-at which time it may vibrate its rattle as a warning (which in this species usually sounds like a high-pitched hiss or an insectlike buzz, with little carrying power). Many Massasaugas seem hesitant to strike unless actually seized or stepped on, while, others are more nervous and strike out immediately at any threatening object, at times without rattling in advance.
Accidental bites to humans are rare and sometimes result from efforts to kill or handle the snakes. Despite having a potent venom, massasaugas can deliver only small amounts at a time through relatively short fangs that often fail to penetrate loose clothing and leather footwear. Curious dogs are far more frequently bttten than people and most survive the experience. Symptoms of envenomation include pain, swelling, and discoloration (due to rupturing of blood vessels) at the bite site, as well as possible systemic reactions (nausea, sweating, fainting). Massasauga bites should always receive prompt medical treatment but serious complications and fatalities are extremely rare.Back to Top
Reproduction and Growth: Eastern Massasaugas mate in both spring and fall. A courting male will align his body with that of the female while rubbing his chin on her head and body; he may also twitch or jerk his body and head. At the same time he attempts to loop his tail around the female's tail and thus bring their cloacas into contact, allowing copulation to occur.
The females give birth to litters of 5 to 20 young in August and early September, usually while they are still in their drier summer habitats. The young are born enclosed in a thin membrane from which they Soon emerge. They may remain near their mother for several days before dispersing. Many females reproduce only every other year. The young snakes reach sexual maturity in their third or fourth year. Captive Massasaugas have lived over 20 years, but the normal life span in the wild is unknown.Back to Top
Conservation: Popu1attons of the little "swamp rattler" have declined rapidly over the last few decades, as its habitats have been converted to human uses, while incessant persecution has reduced their numbers even in the small pockets of remaining habitat. This snake prefers shrubby or marshy lowlands that are immediately adjacent to open uplands. Thus, conservation efforts that focus on preserving wetlands whlle ignoring contiguous upland will fail to preserve this species.
This rattlesnake is generally shy and unaggressive and offers little danger to reasonably cautious people willing to leave them alone. The gratuitous killing of Massasaugas encountered in their natural habitat is needless and regrettable, although their removal from the vicinity of human dwellings is justified. Ironica1ly, Massasaugas found in residential areas are often simply seeking traditional habitats that have been lost to recent development.Back to Top
The above information has been reproduced or complied from the field guides with permission to use such material from the author, James Harding, for the sole use of educating the public on native Reptiles and Amphibians. The field guides used were: