The colubrid snakes are by far the largest group of snakes in the world and in North America. There are 102 species of this type of snake in Mexico, the U.S. and Canada. Colubrid snakes lack what are known as vestigial hind limbs, which are best described as the skeletal evidence of what used to be legs on snakes. As snakes evolved over time, they went from lizard-like creatures with hind legs to their present form, with some types still showing all that remains of what were once those legs in the form of small bumps inside the frame of their skeleton. Most colubrid snakes have only one lung but some species have two, or a much smaller one accompanying a larger lung. The colubrid species are mostly average-sized snakes and include such common snakes as the garter snake, the rat snake, the corn snake, the eastern racer and the hog-nosed snake. These snakes feed on insects and small animals such as frogs, toads, voles and mice for the most part and pose no threat to humans.
The most primitive of snakes that live in North America are the slender blind snakes of the family leptotyphlopidae. These snakes do have vestigial hind limbs and lack the ability to see, with their eyes covered by scales and resembling a tiny dot. The slender blind snakes live underground the majority of the time and dine on insects such as ants and termites. The Western blind snake and another type called the Texas blind snake are the two from this snake family found in North America, living in the southwestern U.S. and Mexico. They are almost worm-like in appearance and rarely exceed 16 inches in length.
Boas & Pythons
Two more species of North American snakes fall under the boidae family hierarchy. This family includes the pythons and the boas, a family that contains many of the world's largest snakes, such as the anaconda and rock python. Although most of the boas live where the temperatures are warm, in North America one of the two species--the rubber boa--has a range that extends all the way from Mexico north into Washington State in the U.S. and as far as British Columbia in Canada. The rosy boa prefers much warmer climates and is found in southern Arizona, California and into Mexico. Boas have two lungs, jaws that open wide to swallow food and vestigial hind limbs.
A venomous snake that possesses a set of fangs in the front of the mouth, the members of the family elapidae found on North American soil include coral snakes and the yellowbelly sea snake. These types are related to the cobras of Asia and Africa and kill and/or paralyze their prey by biting it and injecting venom. This family of snake has many of the same characteristics as the colubrids do and their diet consists mainly of other types of snakes. The other venomous types of snakes in North America belong to the viperidae family. These extremely developed snakes have sensors called pits that detect heat. They lie between the snake's nostrils and its eyes and give these snakes the name "pit vipers." The eyes have an oval shape to them and the fangs that deliver the poison are hinged and fold down when not deployed. The many kinds of North American rattlesnakes including the cottonmouth and the copperhead all are viperidae.