Desert Snake Hears Mouse Footsteps With Its Jaw

Desert Snake Hears Mouse Footsteps With Its Jaw



The horned desert viper rests its head on the sand to listen for prey. A sand surface wave moves the left and right sides of the jaw independently, and the vibrations travel to the quadrate, stapes

Just a few decades ago, some scientists doubted that snakes could hear at all. Snakes lack an outer ear and external ear openings, making it difficult to understand how the reptiles receive acoustic vibrations.

However, snakes do have an inner ear and a cochlea, and scientists have observed the animals react to auditory stimuli. But exactly how snakes hear without external ears is still unclear. In a new study, physicists Paul Friedel and J. Leo van Hemmen from the Technische Universitat Munchen in Germany and biologist Bruce Young from Washburn University in Kansas have presented a model of how the horned desert viper Cerastes cerastes hears – with its jaws.

While the jaw-hearing method is widely known, the new research uses naval engineering techniques to explain how vibrations from the jaw travel through the head and give rise to sounds in the animal’s brain. The scientists also explain one of the more intriguing parts of jaw-hearing, which is that the snake’s left and right sides of its jaw can move independently in order to localize a sound’s source, such as the location of a mouse’s footsteps.

“Up to now, no one has ever pondered the fact that snakes could use jaw-hearing in stereo,” Friedel told PhysOrg.com. “This is, however, crucial, since stereo hearing is essential for locating a sound source. We have thus explained how jaw-hearing can actually be very informative for the snake, and not simply a system signifying that ‘something is there.’”

As a mouse skitters across the desert sand, its footsteps create surface waves (specifically, Raleigh waves) with a wavelength of about 15 centimeters and amplitude of the order of 1 micrometer. These surface waves are similar to water waves, in the sense that the sand particles (modeled as a continuous medium) carry out an elliptic motion. The wave velocity of the ripples is about 45 meters per second. The frequency of the waves peaks between 200 and 1000 Hz – which falls squarely into the snake’s optimal sensitivity for frequencies of around 300 Hz.

When the horned desert viper has its jaw resting on the sand, the vibrations from the mouse footsteps pass underneath both sides of the jaw. The vibrations travel through the snake’s head through two bones – the quadrate and stapes – and then stimulate the cochlea. The snake’s auditory system can sense jaw movement down to angstrom-sized motions (on the order of a single atom). The scientists determined that the lower jaw amplitude is about half that of the 1-micrometer incoming surface wave – plenty large enough for the snake ear to detect with efficiency.

From the cochlea, the auditory signals are relayed along axonal delay lines to a set of topographically organized map neurons in the brain. The researchers modeled this neuronal network, where every map neuron is tuned with microsecond accuracy to a specific “interaural time difference,” or the time difference between signals received from the left and right sides of the jaw. When a map neuron fires, it corresponds to a specific input direction, enabling the snake to localize its prey with stereo precision.

The hearing model gives strong support to snakes’ unusual way of hearing, showing that the technique is not only possible, but is also a highly efficient survival mechanism. As Friedel explains, the jaw-hearing method offers some advantages compared with the conventional hearing method using outer ears.

“This has to do with the so-called impedance matching problem,” he said. “If air-born sound arrives at a tissue surface, most of the energy will be reflected. This is because the acoustic impedance (which is a measure of how ‘easily a sound wave can be generated’) of air is much smaller than that of tissue (or the inner ear). To solve this problem, the mammalian middle ear possesses three hearing ossicles that transfer the sound from the tympanic membrane through the inner ear. The snake does not have a middle ear with three ossicles, but by using the jaw-quadrate-stapes pathway, the problem of impedance matching is avoided.”

That's remarkable!

Reptile Rescue Den wrote:

That's remarkable!

Yeah, keep you ear to the ground hey.

hahahaha indeedy!

wow! thats amazing, kinda logical when you think about it! do you think it applies to all snakes or just the viper?

All snakes but the viper was being studied for it at the time. A snake can also hear through its stomach as the vibrations on its skin move to the bones in its ear bones that acknowledge the sound.

isn't nature clever!

Humans have that sense as well, well my mothere anyway, I swear she knew exactly when Im slobbered as I try to get into the house

Hahahahahahahahahahahahahaha that is so funny Bogga

Does the arboreal species use a similar mechanism?

Since snakes lack surface ear openings and appeared to naturalists to be indifferent to sound, many have assumed that these reptiles are deaf. Commenting on this error, The New Encyclopaedia Britannica (1987, Vol. 27, p. 159) states: “This supposition is incorrect; snakes are sensitive to some airborne sound waves and are able to receive them through a mechanism that serves as a substitute for the tympanic membrane. . . . Moreover, while the sensitivity of most snakes to the middle of the low-tone range is below that of most other types of ears, it is not seriously so. In a few snakes, however, the sensitivity is about as keen as in the majority of lizards with conventional types of ear openings and middle-ear mechanisms.”

Theoretically....snakes are confined to having their whole bodies in contact with a supporting surface. Surely they must have developed a way to 'hear' vibrations through their bodies. If you ever so gently touch a snake's belly it flinches away from your finger, because of this I can assume that their underbellies are incredibly sensitive. Sound waves transfer some of their energy into objects they intercept and that energy becomes vibrations. I think we would be suprised what a snake can actually 'hear'.


Snakes have no external ear; vestiges of the internal structure of the ear are still present in the form of small bones, the stapes, which transmits vibrations to the inner ear. To detect these the lower jaw must be in contact with the ground. The vibrations are then transmitted via the jawbones, the stapes, and the quadrate bone to the inner ear. In addition to the footsteps of an enemy or potential food, snakes can almost certainly pick up low frequency airborne sounds.