The heat recepters are visible just below the eyes here in this southwestern speckled rattlesnake Crotalus m. pyrrhus.

Of course, the tell-tale physical sign of this unique group of reptiles is the rattle - although some island species are beginning to show signs of rattle loss or rattle degeneration. All rattlesnakes also possess a heat receptive pit located on each side of the head just below the nostrils. This character is present in all members of the Crotalinae, and many members of the Boidae family. Studies have shown that this pit can pick up temperature differences as minute as 0.0026° Celsius. The scales on most of the Crotalus are thick and rugose. The individual scales are often distinct and keeled down the middle. Square blotches and diamonds make up the primary pattern for a majority of the species with some variations in between. The eyestripe is also another prominent feature of rattlesnakes. It runs from the corner of the mouth through the eye and helps to camouflage the eye.

Numerous stories of enormous rattlesnakes have been told throughout the years. But what is a large rattlesnake? Which species are the largest? Obviously, rattlesnakes do not attain the enormous lengths of the legendary boas and pythons. But rattlesnakes in general are girthy animals and even a 120 cm diamondback rattlesnake is quite impressive in size. The largest species of rattlesnakes can and do attain lengths over 150 cm with the largest nearing or even topping 210 cm in length. Of the species that are considered large, the eastern diamondback (Crotalus adamanteus) is probably the largest of all attaining both a long length and large size. Species that should also be considered large include the western diamondback (Crotalus atrox), Mexican west coast (Crotalus basiliscus) and the Neotropical rattlesnakes (Crotalus durissus). On the other end of the spectrum, the smallest species include all the members of the Sistrurus genera and many of the montane species such as the Queretaran dusky (Crotalus aquilus), rock (Crotalus lepidus), twin-spotted (Crotalus pricei), Mexican dusky (Crotalus triseriatus) and ridgenose rattlesnakes (Crotalus willardi).

	The Snake River Canyon in southeastern Washington. This talus slide is home to the only rattlesnake in the region, Crotalus o. oreganus. It shares this habitat with the very common Great Basin gopher snake and western racer.	High elevation Pine-Oak forest in southeastern Arizona, U.S.A. These mountains are home to four species of rattlesnakes: Crotalus l. klauberi, Crotalus m. molossus, Crotalus p. pricei and Crotalus w. willardi. Several species also occur in the area in the canyons and flat desert nearby: Crotalus atrox, Crotalus s. scutulatus, Crotalus tigris.
	This desert kingsnake Lampropeltis g. splendida was found on the road feeding on a road-killed Mojave rattlesnake Crotalus s. scutulatus.

Although no clear visible signs exist to differentiate the sexes, rattlesnakes tend to exhibit quite a significant difference between the tails of males and females. Male rattlesnakes of many species have a proportionally much longer tail than females do.

Representatives from this group of thirty or so species occupy numerous habitats throughout the Western Hemisphere. From the desert sidewinder (Crotalus cerastes) that inhabits hot, dry areas such as Death Valley to the dusky rattlesnake (Crotalus triseriatus) which can be found at elevations above 4,000 meters in the mountains of Mexico, rattlesnakes have learned to exploit just about every niche in the Western hemisphere. Habitat types for the rattlesnakes include: deserts, prairies, grasslands, shrublands, canyons, low and high elevation montane forests, riparian zones and swamp.

A majority of rattlesnakes are associated with drier environments such as deserts, desert shrub, prairies, savannahs and dry rocky canyons. Even the South American rattlesnakes (Crotalus durissus) found in what is considered tropical South America are more often associated with the drier areas around the rainforests and not in the rainforests themselves. One of the more diverse groups of rattlesnakes are the montane rattlesnakes which are associated with high elevation forests. Here the environment is more lush, the vegetation thicker and the temperature lower than in the desert. The rattlesnakes mostly associated with moist environments are those in the southeastern United States. These include the pigmy rattlesnakes (Sistrurus miliarius) and eastern diamondback rattlesnake (Crotalus adamanteus).

Rattlesnakes are predators and in some situations, they are one of the top predators in their ecosystem. They feed on a variety of prey items with the primary targets being rodents and lizards. The larger species feed mainly on various rodents and up to rabbits in the case of some of the larger species. Lizards tend to make up the primary diet of young rattlesnakes and the smaller montane rattlesnakes.

Despite possessing a venom that serves well as a defense mechanism, rattlesnakes fall prey to many different predators; of which the most dangerous is man. Rattlesnakes are one of the most feared creatures in the southern United States and are often killed on sight. Rattlesnakes found in the wild, even far from civilization, are quickly dispatched. The saddest sight is seeing the thousands of rattlesnakes collected and slaughtered at Rattlesnake Roundups that still continue throughout the southwestern and southeastern United States. Aside from man, numerous larger vertebrates will make prey out of rattlesnakes. Many raptors will take rattlesnakes as prey. On the mammalian side racoons, skunks, ringtail cats, badgers and many small carnivores readily make prey of rattlesnakes, especially young snakes. One of the most famous rattlesnake predators is a fellow ophidian, the common kingsnake (Lampropeltis getula). This snake is immune to the bite of the rattlesnake and in studies, rattlesnakes have shown an aversion to the scent of the common kingsnake.