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I recently went to Left Fork Rocks in Frederick Municipal Forest in Maryland, and while climbing around I saw a snake. The snake was slithering into a cavity in the rocks, so I could not see its head, but I was able to identify it due to the presence of a rattle at the end of its tail. This is a specimen of the timber rattlesnake (Crotalus horridus). I have posted in general about rattlesnakes before, so in this post I will talk about the structure that makes them unique among snakes: the rattle. Many people find similarities between the noise made by the rattle of rattlesnakes and the noise made by maracas. However, unlike the maracas, the rattle does not have tiny balls inside banging against the wall that contains them. Rather, the rattle is composed of hollow segments made of keratin (the same stuff that makes up your fingernails). When the snake shakes its tail 50 – 100 times per second, the segments strike each other and produce the rattling sound. Every time a snake sheds its skin, it adds an additional segment to its rattle, but because the segments of the rattle can become damaged and fall off, the number of segments in a rattle are not a measure of the age of the rattlesnake or of the total number of times it has shed its skin.  The function of the rattle is to protect the snake against animals that may inadvertently harm the snake and which are too large for the snake to eat. But how did rattlesnakes get their rattles? One hypothesis is based on the fact that many snakes shake their tails when threatened. Scientists have found that those snakes which are closely related to rattlesnakes shake their tails in a manner that is similar to that of the rattlesnake. Thus, it is suggested that this behavior was a signal precursor that allowed for the selection of snake rattles once they developed. One last interesting fact about the rattle of rattlesnakes is that the snake can’t hear the sound they make with their rattles! Rattlesnakes have inner ear structures which are attached to the lower jaw (they don’t have an eardrum or an external ear like we do) and can sense vibrations transmitted through the ground. Rattlesnakes can perceive airborne sounds that produce vibrations in their bodies, but their overall ability to hear sounds is limited compared to humans. The photograph belongs to the author and can only be used with permission.
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In our cultural ethos, rattlesnakes are inextricably linked with the wild west of tumbleweeds, cowboys, horses, sheriffs, and outlaws. These reptiles are indigenous to the Americas and have several notable features. The most distinctive is the rattle at the tip of their tails which they can move 60 or more times per second producing a sound which serves as a warning of their proximity. Rattlesnakes are deaf, but they compensate for this by having a highly developed sense of smell. In fact, the reason why rattlesnakes (and other snakes) constantly stick their tongues in and out of their mouths is to bring scent particles in contact with their smell organs which lie in the roof of the mouth. Rattlesnakes do not hear sound, rather they have an inner ear that is very sensitive to vibrations in the ground which are transmitted to it by the snake’s muscles and jaw bones. Besides also having very good vision, rattlesnakes have the ability to sense heat thanks to organs located behind each nostril which gives the snakes the ability of heat vision allowing them to hunt in the dark. Rattlesnakes have a venom which they inject through their fangs when they bite much in the same way that a hypodermic needle works. The venom consists of proteins that break down cells and tissues, as well as anticoagulants and neurotoxins that cause circulatory arrest and respiratory paralysis. The Timber Rattlesnake (Crotalus horridus) featured in the video below was filmed at the Zoo Knoxville in Knoxville, Tennessee. |
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