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Crotalinae: The Crotalinae, or crotalines, are a subfamily of venomous vipers. They are distinguished by their heat-sensing pit organs located between the eye and the nostril on either side of the head. 18 genera are currently recognized: :[2] 7 in the Old World and 11 in the New World. Like all viperids, pit vipers all have a pair of relatively long, solenoglyphous (hollow) fangs that are used to inject mainly proteotoxic venom. The head has an obvious triangular shape and eyes have elliptical pupils. The pit organ is clearly visible between the eye and the nostril of this New Mexico ridge-nosed rattlesnake, Crotalus willardi obscurus. Pit vipers are named after their specialized thermoreceptors: heat-sensitive organs located on either side of the head that look like small pits. These pits contain membranes sensitive to infrared radiation and allows the snakes to locate their prey based on temperature differences with their environment. To a pit viper, rodents and birds that are only fractionally warmer than the background stand out even in complete darkness. It is reported that the snakes can detect a temperature difference of a mere 0.003°C from the background. Like a primitive pair of eyes, these pits even give them depth perception, allowing them to accurately strike warm targets even in complete darkness. However it is not known whether the snake experiences this sense as a visual image or in some other fashion. Since the crotalines, like most other viperids, are nocturnal ambush predators, this adaptation serves them particularly well. In an example of parallel evolution, only the boids have developed similar heat-sensitive organs. Crotalines range in size from small, such as the eyelash viper, Bothriechis schlegelii, with a maximum of 50 cm (20 inches), to the bushmaster, Lachesis muta, that grows to an imposing 3.5 metres (11.5 feet) and is the longest viper in the world. |
