It has been known for decades that rattlesnakes, boas and pythons have so-called pit organs between the eye and the nostril that can sense even tiny amounts of infrared radiation — heat — in their surroundings.
Among pit vipers, the western diamondback rattlesnake, native to northern Mexico and southwestern United States, is in a class of its own, its heat-seeking ability up to 10 times keener than any of its cousins.
Even with tiny patches covering its eyes, the snake has shown the ability to track and kill prey blindfolded.
But exactly how these reptiles detect and convert infrared signals into nerve impulses has remained a mystery, and the subject of sharp debate.
One candidate was the photochemical process underlying vision, whereby the eye sees electromagnetic radiation — visible light for humans — in the form of photons that activate receptor cells, which in turn convert the energy into a biochemical signal to the brain.
Some fish, for example, can see into the infrared wavelength of the electromagnetic spectrum.
But David Julius, a molecular biologist at the University of California in San Francisco, demonstrated in laboratory experiments that a different neurological pathway was at work for the serpentine “sixth sense.”
“In this case, the infrared radiation is actually detected inside the pit organ as heat,” Julius said in a phone interview. “We found the molecule responsible.”
A very thin membrane inside the pit organ — essentially a hollow, bony cavity — warms up as the radiation enters through an opening in the skin, he explained.
Because the membrane is in a hollow space, it is exquisitely sensitive to changes in temperature. …