Like all pit vipers, rattlesnakes like this Timber Rattlesnake (Crotalus horridus) have two organs that can sense radiation: their eyes, and a set of heat-sensing “pits” on their face that enable them to locate prey and strike towards it, based on the prey’s thermal radiation signature. These pits have a relatively short effective range of approximately 1ft, but nevertheless give the rattlesnake a distinctive advantage in hunting for warm-blooded creatures at night.
Rattlesnake eyes, which contain a large number of rod cells, are well adapted to nocturnal use. However rattlesnakes are not exclusively nocturnal, and their vision is more acute during daylight conditions. Rattlesnakes also possess cone cells, which means that they are capable of some form of colour vision. The rattlesnake eye lacks a fovea making it impossible for them to see sharply defined images. Instead, they mostly rely on the perception of movement. Rattlesnake eyes are capable of horizontal rotation, but they do not appear to move their eyeballs to follow moving objects.
Rattlesnakes have an exceptionally keen sense of smell. They can sense olfactory stimuli both through their nostrils, and by flicking their tongue, which carries scent-bearing particles to the Jacobson’s organ in the roof of their mouth.
Like all snakes, rattlesnakes do not have external ear openings, and the structures of their middle ear is not as highly specialized as those of other vertebrates, such as mammals. Thus their sense of sound is not very effective. However, they are capable of sensing vibrations in the ground, passed via the skeleton to the auditory nerve.
Timber Rattlesnake (Crotalus horridus) (by Frupus)