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.