A marsh-dwelling member of the ratsnake group, the western foxsnake, rare in Missouri, is moderately large with distinct brown blotches. The ground color is yellowish, greenish brown, or tan, with an average of 37 large brown blotches on the back and smaller ones on the sides. The head of foxsnakes may show some orange color, which might cause them to be misidentified as a copperhead. The belly is normally yellow, marked with a distinct black checkered pattern. When threatened, a foxsnake will vibrate its tail, coil with head and neck raised, and strike repeatedly to defend itself. When captured, foxsnakes give off a musky odor like the scent of a red fox, accounting for their name.
Young lack the yellow ground color and are gray with bold dark brown or black blotches. The head is boldly marked with a black mask running through the eyes and slanding back to the angle of the jaw. There are also black markings on top of the head and large black spots along the upper lips.
Hatchlings resemble western ratsnakes (black rat snakes). Counting ventral scales (belly scales, from neck to anus) is the best way to distinguish them (about 216 on foxsnakes, and about 221 on young western ratsnakes).
Similar species: The eastern foxsnake (P. vulpinus) is extremely similar to the western foxsnake. In Missouri, these two species are mainly identified by their different geographic distribution: the eastern foxsnake occurs only in a few counties along the Mississippi River floodplain north from St. Louis, while the western foxsnake is restricted to a few counties in the northwestern corner of the state. The eastern species has an average of 43 dark blotches on the back and sides with a brown to reddish-brown head.