Some animals and insects on earth can see types of radiant energy that are outside of the range visible to humans. Some types of snakes called pit vipers can see in the infrared. Pit vipers are able to find small animals to eat even in the darkness. They see the infrared light given off by the animals.
Watch the quicktime movie to see how they do it.
Pit vipers have small pits alongside their face that are used to feel the infrared radiation. As they shift their head from side to side they find the small animal by determining the direction of the most intense radiation.