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How do pit vipers detect infrared radiation from warm-blooded prey?

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Compound eye — Senses Vespid wasps (Vespidae), similar to other insects, have compound eyes that consist of thousands of tiny optical units known as ommatidia, which contain light-sensitive photoreceptor cells.

Pit vipers detect infrared radiation through specialized pit organs located on each side of the head, positioned between the nostril and the eye. These organs function as highly sensitive thermoreceptors that allow the snake to "see" heat images of warm-blooded prey.12

Each pit consists of a cavity containing a thin, densely innervated membrane suspended between the walls of the pit. This membrane is extremely thin, which minimizes its heat capacity and enhances the snake's sensitivity to rapid thermal changes. The membrane is supplied with a rich network of nerve fibers that discharge impulses when heat energy reaches them.23

Because the pits are located on both sides of the head, they provide a form of binocular vision, enabling the snake to localize the position of a heat source and accurately direct its strike. These receptors are so sensitive that they can detect temperature differences of less than 0.6 °C (1.1 °F), allowing the snake to identify and target prey even in total darkness.123