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Water moccasins (Agkistrodon piscivorus), also called cottonmouths, are members of the reptilian family Viperidae. They're found in the southeastern United States and as far west as Texas. These large, semi-aquatic pit vipers are aggressive and capable of delivering a lethal strike to humans and other animals. Keenly aware of their environment, water moccasins adeptly hunt, stalk and evade predators, thanks in part to their split, or forked, tongues.
The forked tongue of water moccasins and other snakes is part of a complex system of perception that enables them to navigate their environments with extraordinary acuity. It's such a vital instrument of survival that it's protected in its own enclosure. If a snake's mouth is wide open, only the split tip of the tongue is visible, because most of it's concealed in a sheath in the lower jaw. When the tongue is flicked, it passes through a notch in the jaw called the rostral groove, allowing the snake to flick its tongue without opening its mouth.
Water moccasins' forked tongues work in conjunction with two tiny, bulb-shaped structures on the roofs of their mouths called the vomeronasal system. Equipped with chemoreceptors, the vomeronasal system analyzes pheromones, which are chemical messengers emitted by animals. As the water moccasin's tongue spirals out of the rostral groove, the two forked tips spread wide, picking up pheromones to the left and right. Each time it's retracted back inside the mouth, it transmits the information to the vomeronasal organs, which transmits them to the brain, informing the water moccasin's next move.
Whether out for an evening slither, on a dinner run or looking for love, the water moccasin repeatedly flicks its tongue into the air, collecting all the information it needs. If there's a rat 5 feet to the left, the left fork of the water moccasin's tongue picks up pheromones, transmitting it to the brain via the vomeronasal system. The water moccasin moves slowly to its left, honing in on the rat that has been detected, and strikes. The rat may not die immediately. It runs, the poison slowly taking over its body. Using the receptors on its tongue, the water moccasin patiently tracks the rat, waiting until it succumbs to the toxins before consuming it. In the same way, water moccasins are able to avoid the mongoose in the bushes, conceal themselves from a circling hawk or locate possible mates.
The Mythical Snake's Tongue
Age-old myths abound concerning the snake's mysterious forked tongue. During the late 18th and early 19th centuries, many believed that snake tongues held magical powers against poison. Jars of forked tongues filled the medicine cabinets of the elite classes. Another myth -- one still held by many -- is that the snake tongues contain venom, which is transmitted when the tongue simply touches a target. Some believe that the tongue is a weapon, that its two forked tips are hard, pointed stingers. None of these tales are true, of course, but they do nothing to ease the exaggerated fear of snakes held by so many.
- PetMD: Why Do Snakes Use Their Tongue?
- Indiana Public Media: Why Do Snakes Have Forked Tongues?
- Smithsonian National Zoological Park: Cottonmouth
- Animal Diversity Web: Agkistrodon piscivorus
- Indiana Public Media: A Snake’s 6th Sense: The Vomeronasal System
- Bryn Mawr College: Sixth Sense: The Vomeronasal Organ; Jason Bernstein
- Jupiterimages/Photos.com/Getty Images