This is by far the largest and most common family of snakes, with close to 2000 species found on all the continents except Antarctica. They are usually slender snakes, and in most species the head is not much wider than the body. Maximum length in this family varies from less than 20 cm to over 2.5 meters, but most adults are half a meter to a meter long. Because it is such a big family, there is a lot of variation in the biology of different species. Some live in trees, some underground. Some specialize in certain prey, some eat any small animal they can find. Some lay eggs, some give birth to active baby snakes. A few desert or tropical species are venomous, will small fangs in the back of their mouths, but none of the colubrids of the eastern United States are dangerous to humans.