THE PIT VIPERS
Our poisonous Texas snakes belong to two families—the Viperidae (subfamily Crotalinae—pit vipers) and the Elapidae (cobra-like snakes). The pit vipers, which include rattlesnakes, copperheads and cottonmouths, possess an opening on either side of the head, between the eye and the nostril. With these heat-sensitive pits, the snake can locate warm-blooded prey in the dark and make a direct hit upon a rat or mouse which it cannot see.
Snakes belonging to this family are further characterized by the possession of elliptical eye pupils, somewhat triangular-shaped heads and long, movable fangs in the front of the upper jaw. Each fang is connected by a tube to the poison gland located just behind the eye. When the snake is at rest and its mouth is closed, the fangs lie folded back against the roof of the mouth. During the strike, the mouth is opened so that the upper and lower jaws form an angle of nearly 180 degrees. The fangs are then erected to point almost directly forward. With the fangs in this position, the strike results in a stabbing action rather than a true bite.