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Massasauga Rattlesnake - Sistrurus catenatus PDF Print E-mail
 A Field Guide to Amphibians and Reptiles of Iowa


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See the Minnesota HerpNet Site for more about the Massasauga Rattlesnake  


Massasauga rattlesnake, Sistrurus catenatus
Massasauga Rattlesnake, Sistrurus catenatus, Wisconsin specimen

ENDANGERED. It is illegal to kill or collect this species by law in Iowa. Reports are needed for parts of western, southern, and eastern Iowa. Please report any sightings to us.


This is a small rattlesnake that measures 17 - 39 1/2 inches in length (Conant and Collins, 1991). It is VENOMOUS! There is a row of black or dark brown middorsal blotches on a lighter brown or gray background. There are two or three rows of small spots on the sides. All blotches and spots may be outlined in white. The blotches usually turn into rings on the tail. There are usually five rings that are 3 - 3 1/2 scales wide and 11/2 scales apart. There is a rather broad dark stripe from the eye past the angle of the jaw. The belly is mostly black with irregular white or yellowish marks. Melanistic specimens are known; these specimens are uniformly black dorsally and ventrally. There are usually some light markings on the chin and throat that remain, however.

Massasauga rattlesnake, Sistrurus catenatus, Scott County, Iowa
Massasauga Rattlesnake, Sistrurus catenatus, from Scott County, Iowa

Massasaugas are stout bodied snakes with a triangular shaped head. The pupils are vertically elliptical and there is a heat sensitive pit located between the eye and nostril. This pit is larger and positioned lower on the face than the nostril. There is a rattle at the end of the tail. The rattle is comprised of a series of interlocking keratinous segments that make a buzzing noise when the tail is vibrated. The scales are keeled and the anal plate is single.

This snake may be quite difficult to distinguish from the harmless western fox and water snakes. One may look for a rattle at the end of the tail, but massasaugas usually have small, dark rattles that are not always distinctive. Massasaugas will rattle with their tails off the ground (though not as high as other rattlesnake species). Harmless snakes that vibrate their tails must hold their tails close to the ground to produce noise. The best thing to do is leave it be if you are unsure of the species.

Close-up, Massasuaga rattlesnake
Massasuaga Rattlesnake, Sistrurus catenatus, close up of head, Wisconsin specimen


Two species, the eastern massasauga, Sistrurus catenatus, and the western massasauga, S. tergeminus, occur in Iowa. The eastern species occurs in very few, small marshy areas in eastern Iowa. A small population of the western species is found in southwestern Iowa. These two species were formerly recognized as subspecies in Iowa. Though separate, I have left them in the same account for now.


Massasaugas are extremely rare in Iowa. There were larger populations in eastern Iowa, and throughout southern Iowa. Today, these populations are reduced to less than a half dozen scattered about eastern and southeastern Iowa, and in southwestern Iowa.

County Records for the Massasuaga rattlesnake in Iowa
County Records for the Massasuaga rattlesnake in Iowa

If you see a massasauga in Iowa, do not kill or harm it in any way. Also, do not attempt to catch or move it. It may be a useful record, however. If you wish to report it, try to take a good picture of it. If the specimen is found dead, the specimen will be useful. Be advised that reflex actions, which may occur even hours after death, could result in a fatal bite. They are also an endangered species in Iowa and the specimen must be turned over as soon as possible. A good photo of a dead snake will suffice! Most importantly, give clear and exact locality documentation, and report it to us!


Massasauga rattlesnake, Sistrurus catenatus
Massasauga Rattlesnake, Sistrurus catenatus, Wisconsin specimen

Massasaugas prefer low, swampy areas close to marshes, lakes, and rivers to overwinter. This is the habitat in which I find them in Iowa in spring and fall. They disperse to higher ground into open grassland and prairie habitats in summer. Unfortunately, not much of this habitat remains, especially connected to marshes and other water. Habitat fragmentation and lack of favorable habitat is a primary threat for this species. Individuals may be found in open grasslands, meadows, or dry woodlands, even farms during summer. Bailey (1944) found specimens well away from water when they had a more expansive range in the state.Crayfish burrows are extremely important overwintering structures for massasaugas.


Some references state that massasaugas are slow, sluggish snakes that are quite passive and slow to rattle or strike. They rely on their coloration for camouflage to avoid detection. One may almost step on this snake before provoking a reaction from it. I have found that they are diverse in their behavior as some will rattle at the least provocation and strike repeatedly. One specimen, however was found after a friend had stepped right over it. It did not rattle until afterward when I tossed a cover board on it! The massasauga's rattle is small, and sometimes can only be heard at relatively close distances.

Massasauga rattlesnake, venter, Scott County, Iowa
Massasauga Rattlesnake, Sistrurus catenatus, venter, from Scott County, Iowa

This snake is generally diurnal except during extremely hot weather. They seem to enjoy warm overcast weather as this is the condition under which many specimens were found. Mornings are a good time to look for basking massasaugas. They take shelter under rocks, logs, pieces of bark, under piles of brush, muskrat houses, or in crayfish burrows.

They breed in the spring and fall. They may only breed every other year or less and are sexually mature at the age of three or four. They give birth to living young (ovoviviparous). The young number from 5 - 24 and are about 5 - 7 inches in length. The young are equipped with fangs and are venomous as soon as they are born. They are usually brighter colored than the adults. Instead of overwintering communally like many species of snakes, they overwinter alone in mammal, or, much more commonly, crayfish burrows where they can gauge the water line. It is reported that they emerge with the spring flooding and basically follow the water line during this time.

Massasauga rattlesnake, Scott County, Iowa
Massasauga Rattlesnake, Sistrurus catenatus, juvenile, from Scott County, Iowa


The diet of the massasauga is comprised largely of small mammals, but small birds, lizards, frogs, toads, and other snakes are also consumed. While adults usually feed upon mice, small snakes are an important food item for young massasaugas. It is interesting to note that this snake will bite and release adult mice then search them out and swallow them after they are dead. When birds and lizards are to be consumed, they are held in the snake's jaws until the venom takes effect.


An eastern massasauga from Bremer County, Iowa


An eastern massasauga from Bremer County, Iowa


An eastern massasauga from Bremer County, Iowa



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