Snakes are commonly perceived as silent creatures, yet they possess distinct mechanisms for acoustic communication. These sounds are not vocalizations, as snakes lack vocal cords; instead, they are mechanical noises produced primarily for defense. The most recognized are the hiss and the rattle, but snakes also employ specialized techniques that convert a silent threat into an audible one. Understanding these audible warnings provides insight into the biology and behavior of these reptiles.
Hissing: The Universal Warning Sound
The hissing sound is the most widespread form of acoustic defense across nearly all snake species, serving as a general warning to potential threats. This noise is produced through a specific biological mechanism involving the snake’s respiratory system. It is generated by the rapid, turbulent expulsion of air through the glottis, which is the small, slit-like opening to the snake’s trachea located on the floor of the mouth.
When a snake feels threatened, it will take a deep breath, often inflating its lungs, and then rapidly force the air out. The air rushing across the glottis creates the characteristic “hiss” sound, which can vary in volume and duration depending on the snake’s size and the amount of air it expels. Some species, such as the American bull snake (Pituophis), have evolved an erectile cartilaginous keel located just in front of the glottis. This structure acts to amplify the sound, making the hiss of the bull snake particularly loud and often raspy, sometimes even mimicking the sound of a rattle. Hissing is a low-energy, immediate warning that communicates distress and a readiness to defend itself.
Rattling: A Specialized Tail Appendage
The distinctive sound of rattling is unique to the genera Crotalus and Sistrurus, the true rattlesnakes, and represents a highly specialized form of acoustic warning. The rattle itself is a complex structure composed of a series of interlocking, hollow segments made of keratin, the same protein found in human fingernails. These segments are loosely connected and remain attached to the tail tip after each shedding of the snake’s skin.
The loud, buzzing sound is produced when the snake contracts specialized, extremely fast-acting “shaker” muscles in its tail. These muscles cause the keratin segments to vibrate against one another at a high frequency, which can be sustained for hours. The hollow nature of the segments acoustically amplifies the sound, allowing the warning to be heard from a distance. The rattle functions as an advanced warning system, primarily intended to deter large, hoofed animals like bison or elk from accidentally stepping on the snake. A common misconception is that the number of segments indicates the snake’s age, but this is inaccurate because a new segment is added every time the snake sheds, which can happen multiple times a year; moreover, the fragile terminal segments can break off.
Stridulation and Other Unique Noises
Beyond the hiss and the rattle, many snake species employ unique, mechanical methods to create sound, often through physical contact with their own bodies or the environment. The most notable of these is stridulation, a sound produced by rubbing specialized scales together. This defense is characteristic of the saw-scaled vipers (Echis), which inhabit arid regions.
When threatened, the saw-scaled viper coils its body into parallel, C-shaped loops and rapidly rubs its keeled, serrated scales together. This action generates a continuous, sizzling or rasping sound. Stridulation is thought to be an evolutionary adaptation to conserve moisture, as it avoids the water loss associated with forceful hissing in dry environments.
Other Acoustic Defenses
Other acoustic defenses include cloacal popping, a sudden, loud expulsion of air and waste material from the cloaca, which is a startling defensive reaction. Additionally, some snakes, like certain rat snakes, may rapidly vibrate their tails in dry leaf litter or brush, creating a rustling sound that mimics a rattlesnake. A few species, such as the King Cobra, have a modified respiratory structure that enables them to produce a low-frequency rumble or growl.