by Jennifer Greene
All photos by author unless otherwise noted
Can Snakes Hear?
If you keep one snake or one hundred snakes, chances are you have some opinion on whether or not your scaly friends can hear you. Some keepers are aware that studies have shown that snakes can most certainly detect vibrations in the ground, helping them determine if there is prey or a potential predator nearby. Snakes lack an outer ear, leading some to believe that snakes are completely deaf to airborne sounds. While the lack of a visible external ear likely limits the snake’s ability to hear airborne sounds, they do have a system of hearing that includes an inner ear. Their hearing system is, in its own way, both simpler and more complex than our own, and by no means is it out of the question that a snake can hear airborne sounds. Mostreptile keepers have their own opinions and knowledge of the seeming simplicity of a snake’s hearing abilities, but the reality of their sense of hearing is that it involves a wider range of the sense than our own. They may not be able to hear the range of audible frequencies that we can, but they can sense sound in a way that is alien to us.
Anecdotally, it is not difficult to find keepers that swear their snakes can hear them. Walking through a reptile show and asking various reptile enthusiasts if their snakes can hear them will give you the full gamut of stories about the phenomenon. You will hear everything from someone assuring you their snake knows its name and comes when it’s called to others, assuredly too professional and experienced for such nonsense, confidently assuring you that snakes are deaf and cannot hear a word you’re saying.
Studying snake hearing and being able to provide definitive proof one way or the other ultimately requires more than the average keeper’s call for supper or similar, haphazard and informal tests. Older experimental methods tracked electrical activity in the brains of snakes in several families when sounds at various frequencies were played; a more recent (and less invasive) study looked at the reactions of one rattlesnake species to sounds played at various levels. Interestingly, the older experiments show that snakes have two sensory systems that detect both sound and vibration, and note that while each system detects primarily one or the other, the range for each overlaps (Hartline 1970).
Before moving forward, a quick overview of sound and hearing may help you, the reader, to better understand how snakes are capable of hearing even without an external ear, and why it is relevant that a snake’s hearing includes both airborne sound and vibrations. First, let’s look at sound: sound is a pressure wave through a medium, caused by vibrations. Everything vibrates slightly at a molecular level, however, those tiny vibrations are usually too quiet for us to hear. What we usually perceive as sound to our ears is a sound wave within a certain frequency – a vibration happening at a certain speed through the air.
Human ears perceive sound within a specific range based on what the bones in our ears can pick up and then translate to vibrations within the deepest part of our inner ear. The cochlea is the spiral tube within our ear, and the microscopic hairs within the cochlea pick up specific frequencies of sound – each hair correlating to a different frequency. All of that translates to our ability to hear a wide range of audible sound, typically 20 to 20,000 hertz (the measurement of the specific frequency of a sound wave). Snakes hear not just what we consider audible sound; their entire body acts as an organ to pick up vibrations – and their brain processes these vibrations in a similar part as audible sound, creating a sense of hearing considerably different than what we experience as mammals. (Hartline, 1970) It is not as wide as our own, but it is experienced in a much, much different way.
Continuing, if airborne sound such as speech is nothing more than vibrations in the air, it stands to reason that snakes may actually be able to hear it. In fact, experiments show that snakes are capable of hearing airborne sound within the mid to lower ranges of normal human speech. (Hartline 1970) While snakes are much more limited than humans and other mammals in their range of perceivable sound, they are capable of hearing sounds in the ranges of 150 Hz to 600 Hz. (Hartline 1970)
Human speech falls almost exactly within that range, even with wide variance in frequency due to age and/or gender. Baby cries can be up to 500 Hz, while children’s voices are anywhere from 250 to 400 Hz, and men and women ranging from 125 to 200 Hz on average, respectively. (www.ncvs.org)
With snakes having this almost alien method of picking up sound, and both of their sound detection systems overlapping in terms of detecting both airborne and physical vibrations, it makes it hard to conduct experiments to determine if snakes are not just perceiving airborne sounds but also capable of understanding and reacting to them. A recent study has found that snakes can perceive and react to airborne sound by using a soundproof enclosure and a specially designed hanging basket to minimize vibrations from the surface. Using the notoriously cranky Western Diamondback Rattlesnake as the test subjects, the experimenters found that 92% of the time, the snakes reacted in one or more ways to airborne sounds. (Young and Aguiar, 2002) Their testing methods were not able to determine if the snakes could identify the direction of the sound, but did conclusively show a reaction to purely airborne sounds. Another study compliments this information with the observation that another crotalid species, the Saharan Sand Viper, utilizes its sense of vibration to determine the direction of an object that is causing sound, providing “evidence that snakes are capable of hearing, albeit, perhaps, in a unique sense of that term.” (Young and Morain, 2001)
All of this information culminates in the conclusive statement that YES, snakes can in fact hear airborne sounds in addition to sensing vibrations in solid objects. Their sense of hearing, while limited in frequency, does encompass a wider range of potential stimuli to help a snake understand what is going on in its environment. While they are not quite adapted to understand speech, the ringing of a dinnerbell, or similar acoustic triggers, they are capable of hearing that these things are taking place. When considering if a snake’s lack of understanding that you are speaking to it makes it lacking in intelligence, do also consider that there is no reason for a snake to understand human speech. Everything in its sensory arsenal is to identify what is happening around it, and help it to determine if there is prey, predator, or something to ignore happening around it. A snake lives a much simpler life than the average mammal, and what they do with their complex array of senses reflects this. Just because a snake doesn’t react to you talking doesn’t necessarily mean it didn’t hear you; chances are, it just wasn’t something the snake considered worth reacting to.
Young, B.A. , Aguiar, A. (June 27th, 2002) Response of western diamond back rattlesnakesCrotalus atrox to airborne sounds
The Journal of Experimental Biology, 205, 3087 – 3092
Young, B.A., Morain, M. (December 10th, 2001) The use of ground-borne vibrations for prey localization in the Saharan sand viper (Cerastes)
The Journal of Experimental Biology, 205, 661-665
Hartline, P.H. (August 18th, 1970) Physiological Basis for Detection of Sound and Vibration in Snakes
The Journal of Experimental Biology, 54, 349-371
Factors Influencing Fundamental Frequency, retrieved July 18th, 2013 fromhttp://www.ncvs.org/ncvs/tutorials/voiceprod/tutorial/influence.html