The small-mouthed salamander averages four to five and one-half inches in length. It has a small mouth and head. There are two color variations: the dark variation has an indistinct pattern while the other variation has black and gray speckles on a black background. The belly is black.
The small-mouthed salamander may be found in the southern two-thirds of Illinois. It lives in woodlands, prairies, swamps, river floodplains and farm fields. This salamander may be found under objects or in burrows. It is active at night. Breeding occurs from late February through March. Eggs are deposited on sticks or vegetation in masses of six to 30 in any standing body of water. Some smallmouth salamanders breed in streams. Each female may deposit from 300 to more than 800 eggs. Eggs hatch in a few days. Larvae transform into land-based adults from late May through July. This salamander eats earthworms, slugs and arthropods (spiders, insects, mites and others).