Human eyes don’t respond to infrared, the color beyond red on the rainbow. But some animals are able to detect infrared waves, which radiate from warm objects.
That includes venomous snakes from the subfamily Crotalinae, commonly known as pit vipers—so-called for the pair of heat-sensing organs located in “pits” between their eyes and nostrils. A thin membrane within these receptors connects to the brain at the optic nerve, and having two of these front-facing organs helps them to triangulate in total darkness the direction and distance of warm-blooded prey, which radiate infrared.
But while other animals use infrared detection to navigate their surroundings—fire chaser beetles use infrared sensors to locate forest fires where they prefer to lay their eggs—these snakes use it hunt. To a rattlesnake moving in the dark, the heat of a tiny mouse is a bright beacon signaling its next meal.
Heat Gene
Scientists have long known that this group of venomous vipers—which include species of lanceheads, moccasins, and bushmasters—have the ability to sense infrared at a distance of about 1 meter. But in 2010, a study in Nature shed light on the molecular process behind the snakes’ “night vision.”
By examining the nerve receptors in rattlesnake pit organs, researchers found that they produce the same protein that detects chemical irritants in other species—including humans. But in rattlesnakes, these “wasabi receptors” have evolved to detect heat.
Pit Organs in Other Snakes
Non-venomous snakes such as boa constrictors and pythons also have heat-sensitive pit organs they use to hunt. But, while boas and pythons have smaller and slightly less heat-sensitive organs located along their lips, they have more of them—in some cases over a dozen. One possible explanation for this anatomical difference may be that having more organs allows these snakes to collect greater amounts of information about their surroundings—an adaptation that may come in handy while they patiently wait for prey to come within striking range.