Illinois Natural History Survey - University of Illinois

Squamata        suborder Serpentes
Elaphe obsoleta -- Gray Ratsnake

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Alexander County, IL; photo by Mike Redmer distribution map

Purple shade indicates vouchered specimens. Light blue (cyan) shade indicates photographic records. Yellow shade indicates verified sighting. Slanted hatch indicates pre-1980 records only

NOTE: Not all specimens upon which these maps are based have been verified.

Key Characters: Sides unusually straight, forming a sharp corner with the belly; back scales weakly keeled; anal plate divided. Juvenile distinctly marked with dark back and side blotches on a white or gray background.

Similar Species: Racer, common kingsnake, plainbelly water snake. Juvenile resembles many blotched snakes: milk snake, young of prairie kingsnake, racer, coachwhip, and water snakes.

Subspecies: Black rat snake, E. o. obsoleta; gray rat snake, E. o. spiloides.

Description: Large (up to 175 cm TL), dark snake with a highly variable pattern that ranges from a series of light blotches to completely black. The groundcolor between blotches darkens with age, obscuring most of them by 80 cm TL, except in extreme southern counties where the subspecies E. o. spiloides retains remnants of the juvenile pattern throughout life. Belly black-and-white-checkered. Adults have white, orange, or red skin between the dark scales.

Habitat: Variety of forest, shrub, and edge habitats. Common around farm buildings and abandoned houses.

Natural History: This arboreal constrictor often suns and prowls on tree limbs and rock outcrops where it feeds on birds, their eggs, and small mammals. Mates in April or June and l0-20 eggs between early May and July. Young (ca. 30-35 cm TL) hatch late July to September. Large adults have few predators other than humans. Carnivorous mammals and raptors are the main predators of juveniles.

Status: Locally common, especially in southern counties.


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