What organ do pit vipers use to detect infrared radiation?

Pit vipers use pit organs to detect infrared radiation. These heat-sensitive organs sit in a pair of facial pits between each eye and nostril, giving the snakes a way to sense warm objects even in darkness.

Each pit contains a sensitive membrane that responds to tiny differences in radiant heat. Signals are carried through the trigeminal nerve system and combined with visual information, helping a snake locate warm-blooded prey such as rodents and birds. The system is often described as a form of thermal sensing rather than ordinary vision.

The facial pits are the feature that gives this snake group its common name. Pit vipers include rattlesnakes, copperheads, lanceheads and many Asian species. Their heat sensors can also help them judge a prey animal’s position and, to some extent, its size.

A common mix-up is Jacobson’s organ, also called the vomeronasal organ. That organ detects chemical information collected by the tongue; it does not detect infrared radiation. The brille is simply the transparent scale covering a snake’s eye.