[3] T. proximus is a slender snake with a very long tail, approximately one-third of the total length of the body.

The upper labials are whitish and unmarked, contrasting with the dark top and sides of the head.

[3] Nota bene: A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Thamnophis.

T. proximus is a semiaquatic snake that occurs in a wide range of habitats, usually not far from water.

It feeds on a range of invertebrates (earthworms, crayfish) and small vertebrates (lizards, fishes, and frogs, including tadpoles).