The flat-headed snake averages seven to eight inches in length. Its head is darker than the rest of its body. The back is brown, and the belly is salmon pink. The scales are smooth. Its head is flattened and slightly wider than the neck. The flat-headed snake is the smallest Illinois snake.
The flat-headed snake lives under rocks on bluffs along the Mississippi River. This species spends much time under rocks or in underground burrows. It escapes summer and winter weather by burrowing. Mating occurs in April or May. One to four eggs are deposited in the soil under rocks in June. Hatching occurs in late summer. The flat-headed snake eats small arthropods.