Bullsnake

Scientific name: Pituophis catenifer sayi

A subspecies of the gopher snake, is Yellowstone’s largest reptile, ranging from 50 to 72 inches long.
Yellowish with a series of black, brown, or reddish-brown blotches down the back; the darkest, most contrasting colors are near the head and tail; blotches are shaped as rings around the tail.
Head resembles a turtle’s in shape, with a protruding scale at the tip of the snout and a dark band extending from the top of the head through the eye to the lower jaw.

In Yellowstone, found at lower elevations; drier, warmer climates; and open areas such as near Mammoth.

Lives in burrows and eats small mammals—behavior that gave the gopher snake its name.
Often mistaken for a rattlesnake because of its appearance and its defensive behavior: when disturbed, it will coil up, hiss loudly, and vibrate its tail against the ground, producing a rattling sound.