The gray ratsnake averages 42 to 72 inches in length. The scales in the middle rows along the back are weakly keeled (ridged) while the remaining scales are smooth. Coloration varies in this species. It ranges from plain black, sometimes showing traces of a white pattern when the skin is stretched, to a blotched pattern on a gray or pale brown background. The belly has a checkerboard pattern, the throat is white, and the head is wider than the neck.
The gray ratsnake may be found in the southern two-thirds of Illinois. This snake lives in rocky hillsides, woodlands, thickets, old fields, barnyards and farm land. Active by day except in hot weather, the rat snake climbs readily into trees. It moves slowly and may freeze in place when disturbed. If annoyed, it will raise its head, vibrate the end of its tail and lunge. This snake kills its prey by constriction. In the fall it congregates in places like rock outcrops (where it may hibernate with rattlesnakes and copperheads), mammal burrows, cisterns, wells or rotten tree stumps. Mating occurs in April or June. The 10 to 20 eggs are deposited in rotten wood, sawdust or in soil under rocks between May and July. Eggs hatch from late July to September. The gray ratsnake feeds on birds and small mammals, particularly rodents.