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There are 11 subspecies associated with the North American Racer (C. constrictor) and, with the exception of the high mountains and the arid southwest, they are widely distributed across the United States. The Eastern Yellow-bellied Racer (C. c. flaviventris) ranges from the Great Plains of Montana and North Dakota south to New Mexico and Texas. In Wyoming they are found east of the Continental Divide below 6,500 feet, residing in the prairie and foothills life zones of eastern counties and within the Big Horn Basin. They inhabit regions of the riparian, woodland, sagebrush, and grassland communities that contain a combination of open areas and good cover—usually in the vicinity of water.
As their common name implies, they are fast and agile snakes; however, contrary to the implication of their scientific name, they do not kill by constriction. As active predators, they hunt with their neck and head raised high above the ground to provide a better view of their surroundings, and they vigorously chase down their prey and bite and kill it or consume the food alive. They are diurnal, active from late April through September, and feed on grasshoppers and crickets and other tasty treats such as insects, frogs, other snakes, eggs, and an occasional small mammal. They are often aggressive, exhibit threatening postures or chasing behavior, and will bite repeatedly when handled.
It is a medium sized snake, 2-3 or more feet long (TL) with a slender body and large eyes. Its dorsal surface has smooth scales that are large, oval or irregular shaped, and may or may not be overlapping. The anal plate is divided. Adults have a plain background that is a uniform bluish or grayish green. Juveniles have a broken pattern of many dark blotches, each separated by a pale band, laid down against an olive background; this pattern is lost as juveniles mature during their second year and reach lengths of 20 inches or more. The juvenile coloration is somewhat reminiscent of the adult pattern of the Bullsnake and Great Basin Gopher Snake. The belly is of course yellow.
Mating begins soon after the snakes emerge from their winter dens and after they have had a chance to lie around for a bit basking in the sun. These communal dens may contain large numbers of racers in addition to an assortment of other species such as garter snakes and rattlesnakes. Males are also known to follow the pheromone sent trails left by females. The eggs are laid in clutches of 10-15 and buried in underground cavities and burrows—these too are often communal and may house the reproductive efforts of many females. Hatching requires and incubation period of 40-60 days and young of the year begin showing up in August. Sexual maturity is reached in the 3rd year.