Why do Snakes Flick Out Their Tongue?

Snakes have noses, so why do they flick their tongue to smell? Although they have very sensitive noses, they inhale and exhale so slowly that the scent of their prey quickly escapes them. To combat this, snakes have developed an organ deep inside the mouth called “Jacobson’s organ,” named after Ludvig L. Jacobson, the nineteenth century anatomist who first discovered it. The Jacobson’s organ has two hollows in the roof of the snake's mouth that are lined with chemical receptors perfect for picking up on the faintest of odors. 

A mouse runs by, leaving traces of itself from sweat, skin, fur, and even the gases it exhales. A snake quickly darts its tongue in and out up in the air before touching it to the ground to pick up on these particles, carrying them to Jacobson’s organ and allowing it to zero in on even the quickest of prey. 

This special olfactory auxiliary organ is not unique to snakes though, all reptiles and amphibians as well as some mammals (including humans) have one but their usage varies. Mammals will exhibit what is called a “flehmen” response where the animal will curl back its upper lip and display its front teeth while wrinkling its nostrils to get particles to the organ. (Think of a cat making a funny face.) In many species it is nothing more than a remnant of an organ and is therefore non-functional. 

Scientists once took newborn snakes and exposed them to the scents of various animals to see if from birth they would know which animal was their typical prey. They observed northern banded water snakes darting their tongue most often after detecting the presence of frogs, its typical dietary staple, while queen snakes were the most responsive to the smell of crayfish, their usual favorite. This strongly implies that snakes are born with a particular sensitivity to the smell of certain specific animal species.