Juergen Freund / Researcher Guido Westhoff looking at a cross section of pit organ tissue from a Coastal carpet python (Morelia spilota mcdowelli) through an electron microscope with 20,000 x magnification. Pit organs...

Daniel Heuclin / Wagler's / Temple Pitviper (Tropidolaemus wagleri) showing the thermo-receptive pit organ between the eye and mouth. Controlled conditions. Mindanao, Philippines, February.

Daniel Heuclin / Wagler's / Temple Pitviper (Tropidolaemus wagleri) head in profile showing the thermo-receptive pit organ between the eye and mouth. Controlled conditions. Mindanao, Philippines, February.

Daniel Heuclin / Portrait of Wagler's / Temple Pitviper (Tropidolaemus wagleri) showing heat-sensitive pit organ between eye and mouth. Controlled conditions. Mindanao, Philippines, February.

Daniel Heuclin / Wagler's / Temple Pitviper (Tropidolaemus wagleri) in profile, showing the thermo-receptive pit organ between the eye and mouth. Controlled conditions. Mindanao, Philippines, February.

Daniel Heuclin / Portrait of Wagler's / Temple Pitviper (Tropidolaemus wagleri) showing the thermo-receptive pit organ between the eye and mouth. Controlled conditions. Mindanao, Philippines, February.

Daniel Heuclin / Close-up of Brazilian Lancehead (Bothrops moojeni) showing the thermal sensing "pit" organ between the eye and mouth. Captive. Endemic to Brazil, Argentina and Paraguay.

Pete Oxford / Andean Forest Pitviper (Bothriopsis pulchra) profile showing heat-sensing pit organ, Tapichalaca Reserve, Ecuador

ZSSD / Southern Pacific Rattlesnake (Crotalus viridis helleri) coiled up showing head with sensory pit organ, North America

ZSSD / Red Rattlesnake (Crotalus ruber) portrait showing eye and pit sensory organ, native to North America

ZSSD / Brazilian Lancehead (Bothrops moojeni) snake showing eye and pit sensory organ, native to South America

ZSSD / Brazilian Lancehead (Bothrops moojeni) snake showing nostril and pit sensory organ, native to South America