Rattlesnakes possess a tail like all other snakes, but it is uniquely modified with the signature rattle. This distinctive structure gives these pit vipers their common name. Rattlesnakes belong to the genera Crotalus and Sistrurus and are found throughout the Americas.
Defining the Rattlesnake Tail
A snake’s tail is defined anatomically as the portion of the body located behind the vent, or cloaca. This single opening serves as the exit point for the digestive, urinary, and reproductive systems. Everything from this opening to the end of the body is considered the tail.
The rattle is not a separate attachment, but a specialized terminal segment of the tail bone structure. It is an extension of the final caudal vertebrae, where the scales are modified to form interlocking caps. The tail portion containing the rattle also houses specialized shaker muscles that allow the snake to vibrate the appendage rapidly. Male rattlesnakes tend to have thicker and longer tails than females because they must accommodate the inverted hemipenes.
How the Rattle Forms and Grows
The rattle is composed of a series of interlocking, hollow segments made from keratin. A baby rattlesnake is born with a single scale, called the pre-button, at the tip of its tail. This is replaced by the first true segment, or “button,” after the snake completes its first shed.
A new rattle segment is added at the base of the rattle each time the snake undergoes ecdysis, or skin shedding. As the snake grows a new layer of skin, a new, soft keratin segment forms at the tail’s base. When the snake sheds, the old skin peels away, leaving the newly formed segment attached to the previous, hardened one.
Counting the segments is not an accurate way to determine a rattlesnake’s age. Segments are added with every shed, and a snake may shed anywhere from one to four times a year depending on food availability and growth rate. Furthermore, the brittle, hollow segments frequently break off due to wear and tear, meaning a snake with a full complement of segments is quite rare.
The Purpose of the Rattle
The rattle functions primarily as an aposematic signal, which is a warning display to predators. This loud, distinctive sound is directed at large animals, such as bison, deer, or humans, that might accidentally step on the snake. The rattling is a defensive behavior intended to prevent a physical confrontation that could injure the snake.
Using the specialized shaker muscles to vibrate the tail at frequencies between 50 and 100 times per second is energetically costly for the snake. Therefore, the rattle is deployed as a last resort when the snake’s camouflage fails and a threat has come too close. The ability to rattle allows the snake to conserve its venom, which is needed for hunting prey.
For hunting, the rattlesnake relies on stealth and ambush, utilizing its camouflage and heat-sensing pits to locate and strike small prey like rodents. It does not use its rattle when hunting because the noise would immediately alert its intended meal. The rattle’s function is purely defensive, serving as a clear “stay away” message.