Simultaneous stimulation of the nerves in the severed portion keeps it twitching for a few seconds after separation. Each vertebra of the tails of tail-shedding lizards has a fracture plane that can voluntarily split by the appropriate twitch of the tail muscles. When captured, some lizards voluntarily shed, or autotomize, their tails, which wriggle violently, temporarily confusing the predator and allowing the lizard to escape. The tails of some lizard species are useful in defense in another way. Such a tail swung vigorously from side to side is an effective defense against snakes, especially when the head and body of the lizard are in a burrow or wedged between rocks. Use of the tailĪ few lizards, representing different families, have thick tails covered by large, hard, spiny scales. The effect on skin is negligible the eyes, however, may be severely damaged, and blindness can result unless the venom is washed out quickly. A spitting cobra usually raises its head and the forepart of its body in the characteristic cobra defensive posture prior to spitting, but venom can be ejected from any position. At the moment of ejection, the mouth is opened slightly, and a fine stream of venom is forced out of the fangs by the contraction of the muscle enveloping the poison gland. Instead of a straight canal ending in a long opening near the tip of each fang as in most cobras, the specialized fang of the spitting cobra has a canal that turns sharply forward to a small round opening on the front surface. The spitting of venom by some Asian and African cobras ( Naja) and the ringhals ( Hemachatus haemachatus) is a purely defensive act directed against large animals. Some turtles, particularly the softshell turtles of family Trionychidae and snapping turtles of family Chelydridae, bite frequently and vigorously. Although small lizards have a bite that is effective against only the smallest predators, a large monitor lizard ( Varanus) can inflict a painful wound with its large teeth and strong jaws. For example, the tokay gecko ( Gekko gecko) of Southeast Asia bites if sufficiently threatened. Many lizards, regardless of family and size, also bite in defense. To strike again, it raises its head and neck once more such aggressive, defensive movements of cobras are slower than those of pit vipers. ![]() From the typical raised posture, a cobra sweeps its head forward and downward to bite. ![]() From this position, the head can be rapidly shot forward, stab the enemy, and be pulled back in readiness for the next strike. Vipers and pit vipers usually strike from a horizontally coiled posture. Most of the dangerously venomous snakes ( vipers, pit vipers, and cobras) bite in self-defense. Among the nonvenomous snakes of North America, few are as quick to bite as the water snakes of genus Nerodia however, they are nonvenomous. Others (such as the hognose snakes ) strike with their mouth open but do not bite, but snakes of many species will strike and bite viciously. Some snakes (such as DeKay’s snake ) strike, but with their mouths closed. If a threatening posture does not succeed in driving off an enemy, many reptiles may become more aggressive.
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