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Pit Vipers
Nature Bulletin No. 681  May 26, 1962
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

PIT VIPERS
Unfortunately, since early childhood, most people have acquired a horror or a hatred of snakes. They are morbidly curious about notorious kinds such as the cobras, mambas, fer-de-lance and bushmaster; also about the dangerous species native in North America: coral snakes, rattlesnakes, the water moccasin and the copperhead. But the average person knows little about any of those reptiles and the significant differences between them.

There are approximately 2500 species of venomous snakes. Each of them -- except a few kinds with fangs at the rear of their jaws, and the sea snakes -- belongs to one of two families: the Elapidae and the Viperidae or vipers.

The Elapidae have permanently erect, relatively short fangs at the front of the upper jaw. Their venoms are chiefly neurotoxic and, attacking the nerve centers, cause rapid paralysis of the chest and diaphragm. In this family are the coral snakes, kraits, cobras, mambas and, in Australia and New Guinea, about 60 species including the large and very dangerous taipan and tiger snakes.

In contrast, the vipers have fangs that are similarly placed but "hinged" and so long that, when not in use (striking) they must be folded backward against the roof of the mouth, The big chunky Gaboon viper in Africa may have fangs nearly two inches long. Further, the vipers have venoms consisting mostly of a hemotoxin that destroys the red blood cells and blood vessels.

There are two subfamilies of Viperidae: the true vipers and the pit vipers, The true vipers are found only in Africa and in temperate or tropical regions of Europe and Asia. There is none in Ireland, none in Japan, none in the Americas, and only one species in the Malay Archipelago. C)n the other hand, there are no pit vipers in Africa and no vipers of any kind in Australia and New Guinea.

Pit vipers are distinguished by the presence of two holes, one on each side of the head between the nostril and the eye but lower down than both. They lead to a complex sense organ which apparently assists the reptile -- especially at night -- in locating warm-blooded prey. There are two types of pit vipers: the rattlesnakes -- which occur only in the Americas -- and those without rattles.

Although uncommon or entirely absent in many regions, rattlesnakes are distributed from southern Canada throughout North America, Central America, and South America -- east of the Andes -- as far as northern Argentina. There are 28 species varying in size from the eastern diamond-back (which may become 8 feet long) to a pigmy rattlesnake less than 18 inches in length. The banded or timber or canebrake rattlesnake, the prairie rattler, and the unique sidewinder in our southwestern desert, are some well-known species. Most dangerous, because of its large size and very potent venom, is the tropical rattlesnake.

Other pit vipers without rattles are mostly tropical. They include two giant kinds -- the fer-de-lance, which ranges from the tropical coasts of Mexico to northern Argentina; and the largest of all vipers, the bushmaster, which becomes 11 or 12 feet long. It lives in humid forests, usually near rivers, from Costa Rica to Brazil and also on the island of Trinidad. All other New World pit vipers bring forth their young alive but the female bushmaster lays eggs.


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