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Prairie Rattlesnakes - Crotalus viridis


This is a large, venomous Iowa species that is very heavy bodied and measures from 35 to 45 inches in length; the record is 57 inches. Prairie rattlesnakes have a diamond shaped head which is set off from the relatively thin neck. The pupils of the eyes are elliptical in bright light and there is a heat-sensitive pit between the eye and nostril on both sides of the head. Ground color consists of varying shades of brown, from tan to greenish, to dark brown. There are darker blotches down the back, and smaller spots on the sides. The belly is usually light yellow or cream and unmarked except for darker stippling on some specimens. The tail is ringed with a tan rattle at the end. The rattle at the end of the tail will distinguish this snake from all others in its Iowa range. The scales are keeled and anal plate is single. The subcaudals are single. Young are patterned the same as the adults and some specimens may have a lot of white outlining the blotches. They are 7 to 13 inches in length at birth.

Range & Habitat

Found in North America over much of the Great Plains, from southern Canada south through the United States to northern Mexico. In Canada it occurs in Alberta and Saskatchewan; in the USA in eastern Idaho, Montana, North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, extreme eastern Arizona; in Mexico in northern Coahuila and northwestern Chihuahua. Its vertical range from 100 m near the Rio Grande River to over 2,775 m elevation in Wyoming

Prairie rattlers are found in rolling prairies, grasslands, pastures, and other open prairie areas. The most common habitat utilized by C. v. viridis are the grassy plains, the country of the prairie dog and the burrowing owl.


These snakes seem to emerge from hibernation in late April and early May. Many may be found hibernating together and groups may be seen basking outside the dens in spring and fall. Klauber (1997) gives a detailed summary of dens from South Dakota. They are located on south facing slopes in rocky crevices. In the absence of such structure, they use deep burrows dug by prairie dogs and badgers. These burrows are favored on slight south facing elevations for warmth. During the summer, they move into home ranges. As with many snakes, they are diurnal in the spring and fall, but shift to nocturnal activity during warmer summer months.

Prairie rattlesnakes may not mate immediately following emergence from hibernation as males are reported to locate females away from dens (Rubio, 1998). Males search for females in the latter part of the active season; this species mates from mid-July to early September (Ernst, 1992). Gravid females do not eat during the gestation period and spend most of their time basking. Females give birth from August to early October (Diller and Wallace, 1984). Litter sizes ranges from 6 to 16 young. Unlike Iowas other venomous species, the prairie rattlesnake is pugnacious; coiling and striking with little provocation. This is how many have reacted when I have found them, including specimens from Plymouth County. They will flee if given the opportunity, a bite will not occur if they are left alone when found. Sometimes they sit quietly blending in with the grass, but they are more apt to rattle.

A prairie rattlesnake is easy to identify from other harmless species, even though they are patterned the same. A prairie rattlesnake will hold its rattle high off the ground when it rattles making the rattle very obvious. A harmless snake will vibrate its tail to make a similar sound, but the tail must be held close to the ground to produce any noise; not high in the air like the rattlesnake. This snake is very rare in Iowa and I know of no deaths caused by this snake. Agriculture and human interference have reduced the numbers or this already rare snake. Fortunately, the areas where this snake is now found is difficult to farm and some areas are protected. A prairie rattlesnake found outside of Plymouth County in Iowa should be reported!


Subspecies Common name Geographic range

C. v. nuntius

Hopi rattlesnake

The United States from northeastern and north-central Arizona, from the New Mexican line to Cateract Creek, including the Little Colorado River basin, the southern section of the Apache Indian Reservation, the Hopi Reservation, and the Coconino Plateau from the southern rim of the Grand Canyon to U.S. Highway 66 in the south.

C. v. viridis

Prairie rattlesnake

North American Great Plains from the Rocky Mountains to long. 96 W. and from southern Canada to extreme northern Mexico, including southwestern Saskatchewan, southeastern Alberta, Idaho in the Lemhi Valley, Montana east of the higher Rockies, southwestern North Dakota, west, central and extreme southeastern South Dakota, western Iowa, central and western Nebraska, Wyoming except for the Rockies, Colorado, central and western Kansas, Oklahoma, extreme southeastern Utah, northeastern Arizona, New Mexico, western and southwestern Texas, northeastern Sonora, northern Chihuahua, northern Coahuila.