|EVOLUTION OF PIT ORGANS|
|MORPHOLOGY OF THE PIT|
|PHYSIOLOGY OF THE PIT|
|USES OF THE PIT ORGAN|
|RECENT DISCOVERIES/ RESEARCH|
GENERAL INFORMATION ON PITVIPERS
Pit vipers (Crotalinae) are a subfamily of vipers (Viperidae). They are nocturnal, venomous snakes with large, hypodermic needle-like fangs. Pit vipers tend to be thick, stout snakes with triangular shaped heads and eyes that contain vertical pupils providing clear, sharp vision (Green, 1992). Their size ranges from a foot in length to twelve feet in length (Dowling, 2004). Depending on the habitats in which they are found, pit vipers can vary in color. Arboreal pit vipers can possess vibrant colors, while the terrestrial pit vipers tend to be of earth-toned colorings (Dowling, 2004). In 2004, there had been 16 genera and 157 species of pit vipers identified, however, new species have recently been discovered in Asia (Dowling, 2004). The most easily identifiable pit vipers are the rattlesnakes of the Americas (Dowling, 2004). While pit vipers and other Viperidae are similar in form and function, the most distinguishing characteristic between the pit vipers and the Viperidae is the pit organ located between the eye and the nostril of the pit viper. This organ can sense infrared heat and has proven to be physiologically beneficial to the pit viper.
(Eyelash Pit Viper--Bothriechis schlegelii-Photo courtesy of Snake Pictures)
Geographically, pit vipers are found in Asia, Europe, as well as the Americas. While pit vipers are particularly keen of areas where basking is optimal, there habitats range from the rainforests to the deserts (Greene, 1997). With such a variable habitat preference, pit vipers can beterrestrial or arboreal, while one member, the cottonmouth, is known to be semi-aquatic (Greene, 1992).
Pit vipers tend to give birth to live young (ovoviviparous) while a select few species, the Laschesis, the Calloselasma, and the Trimeresurus, are egg-layers (oviparous). Egg-laying pit vipers usually stick around and defend their eggs (Greene, 1992). Brood sizes can range from two for smaller species of pit vipers to nearly one hundred for larger pit vipers (Greene, 1997).
Some pit vipers are generalists while others are specialists when it comes to prey selection. This is mostly dependent upon the habitat in which the pit viper is found (Dowling, 2004). In general, juvenile pit vipers will consume frogs, invertebrates and lizards (Greene, 1997). As a pit viper grows in size, the size of the prey that they consume will increase. Larger pit vipers have been known to eat mammals ranging from mice, birds, and rabbits to Royal Antelope. Pit vipers can survive and reproduce off of the infrequent eating of large prey items (Dowling, 2004).
Pit vipers are ambush predators. This type of hunting is beneficial in that it requires little energy and it can protects the pit vipers from being eaten themselves since ambushing their prey requires camoflauge (Greene, 1992). As an ambush predator, pit vipers generally hunt at night. Using their tongue (chemosensory organ), pit vipers can locate an area with a high concentration of preferred prey. They then settle into the surrounding area and hide. Using both normal and infrared vision, the pit viper waits for its prey to cross its path at which time it strikes. After striking their prey and injecting their hemotoxic venom, terrestrial pit vipers release it and then track it down using both their chemosensory organs and infrared organs (Dowling, 2004). Releasing their prey is especially important for terrestrial pit vipers. This adaptation protects the pit viper from being attacked by its own prey if it were to hold on to it (Dowling, 2004). On the other hand, the arboreal pit vipers, like the one in the image below, tend to hold on to their prey after a strike since it would be very difficult to track down a bird that has flown off or a frog that has lept from a tree (Dowling, 2004).
(Hutton's Tree Viper--Tropidolaemus huttoni--Photo courtesy of Snake Pictures)