Britannica Sources used in this answer

How do rattlesnakes and pit vipers detect warm prey?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A painted turtle (Chrysemys picta) with a dark shell and red and yellow markings rests on a rock near water, surrounded by green aquatic plants. — reptile Painted turtle (*Chrysemys picta*).

Rattlesnakes and other pit vipers detect warm-blooded prey using specialized infrared receptors located in facial pits—cavities situated on the head below and in front of the eyes.12

These pit organs function as highly sensitive directional distance receptors. Each pit contains a thin, densely innervated membrane that separates two chambers. When infrared radiation from warm prey reaches this membrane, it triggers nerve impulses. Because the pits are positioned on both sides of the head, they allow the snake to localize the heat source and strike accurately, even in total darkness.21

These receptors are exceptionally sensitive to rapid changes in thermal radiation, capable of detecting temperature differences as small as 0.003 °C (0.005 °F). While the pit organs are essential for confirming the identity of prey and aiming the strike, snakes may also use other senses, such as smell and the detection of ground vibrations, to locate their targets.21