How Snakes Listen Without Ears: The Science of Snake Hearing

Snakes may not have ears that stick out from their heads like people, but these legless reptiles have evolved some pretty amazing biological mechanisms that allow them to hear and sense sound in a variety of ways. Snakes don't have external ears, but they do have an internal ear bone called the quadrate that helps them pick up on sound vibrations. They also have other anatomical features, including their jaws, skulls, and skin, that help them sense sounds and vibrations in the air and on the ground.

To learn more about how snakes listen, we'll explore studies from the fields of biology, herpetology, and zoology that have shed new light on this special sensory system. By learning about the ways snakes have evolved to listen without ears, we can better appreciate the many different evolutionary paths animals have taken to meet their basic needs.

How Snakes Hear: The Evolution of Vibration Sensing

Snakes do not have the external ear structures such as the tympanum and eustachian tube that enable hearing in humans and other animals. As a result, their form of hearing is much more attuned to vibrations in the ground than sounds in the air, since sound waves travel faster and with greater intensity through solids than air.

The main anatomical adaptation that makes this possible is the quadrate bone in a snake's jaw, which serves as a middle ear bone by transmitting vibrations from the surface directly to the inner ear. Snakes also use the contact of their lower jaw with the ground to sense vibrations, which are then transmitted through the quadrate bone to the inner ear structures.

Although they don't have the external pinnae (ear flaps) that humans do, snakes have evolved these specialized skeletal adaptations to sense and process the vibrations that travel through their bodies and the ground.

The Specifics of Snake Hearing: Frequency and Sensitivity

Snakes have ear anatomy that enables them to hear low-frequency sounds that generally fall between 50-1000 Hz. Their best hearing sensitivity is between 200-300 Hz, so they can probably hear human speech, which averages about 250 Hz. However, snakes are not good at hearing higher frequencies or airborne sounds in general when compared to humans. Instead, their hearing is best suited for detecting ground-borne vibrations, like the movement of other animals.

According to the studies, different species of snakes have different levels of sensitivity and frequency ranges due to their evolutionary history.

Behavioral Responses to Sound: Curiosity, Avoidance, and Survival

In addition to sensitivity to certain frequencies, more recent studies have shown that snakes have different behavioral responses to different frequencies. For example, some snakes, including the woma python, have been shown to exhibit curious behaviors such as 'periscoping' in response to certain sounds, according to the University of Queensland. Meanwhile, death adders and taipans have been shown to move away from sounds, indicating an avoidance response, according to Discover Magazine.

These responses are likely due to evolution and have been shaped by the need for survival and reproduction, with larger snakes showing less caution and smaller venomous snakes showing more sensitivity to potential predator sounds, according to Popular Science. This knowledge of how snakes respond to sound can help scientists better understand their senses and how they interact with their surroundings.

Ear Loss in Snakes and Lizards: Specializations for Burrowing and Feeding

The absence of external ear structures in snakes and some lizards is a result of evolutionary specializations for burrowing and specialized feeding behaviors, according to the Smithsonian's National Zoo and Conservation Biology Institute. Due to the absence of a tympanic membrane, the stapes (inner ear bone) is surrounded by tissue and attached to the jaw complex, enabling snakes to use bone conduction instead of air conduction for hearing, according to a study published in PMC.

The loss of external ears is a result of evolutionary specializations for behaviors like burrowing and jaw specializations for feeding on specific prey. As the PMC study observes, the absence of a tympanic cavity in snakes seems to be due to their "specialized feeding and burrowing adaptations, which have led to the loss of the external ear structures." Knowledge of the evolutionary factors that led to ear loss in snakes and lizards offers a window into the wide range of adaptations and survival strategies seen in different reptile lineages.

Snakes Use a Multisensory Approach to Integrate Hearing with Other Senses

Snakes use a variety of senses, including hearing, vision, and infrared detection, to interact with their environment, according to research from the Smithsonian's National Zoo and Conservation Biology Institute. Their sense of smell, which is mediated by their tongue and vomeronasal organ, is especially important for finding food and mates.

In addition, many snakes have pit organs that are sensitive to heat, which allows them to form a detailed infrared 'picture' of their environment, according to a study published in PMC. Although snakes' hearing is less sensitive than that of humans, they use it in combination with their other senses to help them make decisions.

This multisensory approach, which includes vibration detection, vision, infrared sensing, and chemoreception, is critical to snakes' survival, helping them interact with their environment and find food and mates. As research in the Journal of Experimental Biology explains, snakes have two separate sensory systems that allow them to detect both air-borne sound and substrate vibration, which further demonstrates the importance of integrating their senses.

Conclusion: The Unique Auditory World of Snakes

In a series of studies, researchers have shown that snakes respond to different frequencies of sound in different ways. For example, some snakes, including the woma python, have been shown to exhibit exploratory behaviors like 'periscoping' in response to certain sounds, according to the University of Queensland study. Meanwhile, death adders and taipans have been shown to move away from sounds, indicating an avoidance response, according to Discover Magazine.

These responses are likely the result of natural selection, with larger snakes being less responsive to sounds and smaller venomous snakes being more responsive to sounds that may indicate the presence of a predator, according to the Popular Science article. Understanding snakes' responses to sounds can help scientists learn more about their hearing and how they use it to interact with their surroundings.