The term worm snake is used for snakes of the Genera Carphophis, Typhlina, and Typhlops. The genus Carphophis is the only one native to North America. Carphophis contains two species, the Eastern Worm Snake and the Western Worm Snake. Some biologists divide the Western Worm Snake into two subspecies; the Western and the Midwestern Worm snake. 'American Worm Snake' is not a technical term, and if you find yourself speaking to a wildlife ecologist, you should use the phrase 'members of the genus Carphophis'
The American worm snakes are the least 'worm-like' of the various species known as worm snakes, looking very much like snakes and not much at all like worms. They got their name not only because they are small, but also because they like to burrow into the ground, and perhaps in part because they eat worms.
American worm snakes are not as small as some other varieties of worm snakes, but they are still much smaller than most snakes; an adult grows to be about 11 inches (28 cm) in length, and remain thinner than the average adult pinky finger. They come in a nice range of Earth tones; brown, black, grey, and pink, with a lighter underbelly. The contrast between back and belly can be quite striking in some cases. They have a small head with no jaw bulge; they are not venomous. They do have an interesting and harmless habit of pressing their pointed tail tip against threatening animals.
The technical difference between the Eastern and Western species is very hard for the layman to distinguish. The coloring on the Eastern Worm Snake (Carphophis amoenus) extends onto the dorsal scale rows one or two, and on the Western (Carphophis vermis) the coloring extends to the third body scale row. However, the Western also tends to be darker, on both back and underbelly, and tends to be black with a pink to red underbelly. This is not a firm distinguishing feature, however.
They prefer to live in the forested hills and Piedmont, although they have spread to some other environments, such as the coastal plains of South Carolina. They are most common in deciduous woodlands. They are technically designated as fossorial, meaning that they prefer to live underground, particularly in rotting logs and leaf litter. They may also be found under rocks, and the Western Worm Snake actually prefers rocky soil.
They feed primarily on earthworms, but they will also eat slugs, snails, small salamanders, and grubs if they come across them. They are hunted in turn by opossum, skunk, fox, various large birds, larger snakes, toads, cats, and even large salamanders.
Eastern Worm Snakes are found in the Eastern U.S., from Rhode Island, and southwestern Massachusetts, down to Georgia and as far west as the Mississippi River. The Western Worm Snake lives west of the Mississippi, from Nebraska and Iowa in the north to Louisiana in the south. Its range does not extend into the prairies or to the west coast.
Some great pictures of Eastern Worm Snakes can be found here.
Pictures of the Western Worm Snake can be found here.