Vampire bats need a blood meal every day or two to survive. And an ability to detect infrared radiation with their noses aids them in their search for sustenance by allowing them to pinpoint areas where blood flows near the surface in their prey. Researchers now report that a heat-detecting molecule on the nerve endings of the vampire bat’s nose is what gives it this ability. Humans have a similar molecule in pain-sensing fibers on the tongue, skin and eyes. The molecule, called TRPV1 in humans as well as bats, is what causes a burning sensation when chili peppers and other spicy foods are consumed, said David Julius, a molecular biologist at the University of California, San Francisco, and the study’s lead author. Although TRPV1 also exists in many other animals, there are slightly different versions of the molecule in each, and it is present in different places in the body. In each case, the molecule is part of a “specialized physiology,” Dr. Julius said. The heat-sensing molecules in the vampire bat’s nose are a good example of mechanisms that evolve in an animal to “detect the things that are most salient to its survival,” he said. Dr. Julius and his colleagues also found that, based on their analysis of the molecule, the bat appears to be related to horses, dogs, cows and moles. This supports other recent research, though previously some scientists believed that the bat, with its furry, rodentlike face, was more closely related to rats and mice. The scientists reported their findings in the current issue of the journal Nature.