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How do rattlesnakes and pit vipers use facial pits to find warm prey?

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thermoreception in polar bears — Thermoreception Warm-blooded animals, such as polar bears, maintain stable body temperatures and adapt to substantial geographic and seasonal temperature fluctuations. Thermal adaptation is supported by the function of sensory structures called thermoreceptors.

Rattlesnakes and other pit vipers utilize specialized facial pits to function as highly sensitive thermoreceptors, allowing them to detect and strike at warm-blooded prey in the dark.12

These organs are cavities located on the head, below and in front of the eyes. Each pit contains a thin, densely innervated membrane suspended between the walls of the cavity. This membrane is extremely sensitive to infrared radiation; because it has a very low heat capacity, it can detect rapid changes in thermal energy—even as small as 0.003 °C—while remaining largely insensitive to steady background temperatures.21

The pits act as directional distance receptors. By receiving heat radiation through the narrow pit opening, the snake can localize the position of a heat source. When warm prey enters the snake's range, the resulting increase in nerve impulse frequency allows the snake to confirm the prey's identity and accurately direct its strike. This system is particularly effective for nocturnal hunting, where the snake combines thermal data with other sensory inputs to target prey.21