It’s time to end a myth. Snakes aren’t deaf to airborne sound, they actually use hearing to help them interpret the world, researchers have now shown. Scientists worked with a group of snakes from seven different species and found they not only have airborne hearing but also react differently to what they hear based on the species.
Experts have long known that snakes can feel sound vibrations through the ground, which is called tactile sensing. However, they have been puzzled over whether they can also hear airborne sound vibrations, and particularly over how they react to sounds. Now, this new study shows how hearing plays a key role in a snake’s sensory repertoire.
“Because snakes don’t have external ears, people typically think they’re deaf and can only feel vibrations through the ground and into their bodies,” study co-author Christina Zdenek said in a media statement. “But our research, the first of its kind, found they do react to soundwaves travelling through the air, and possibly human voices.”
How snakes respond to sounds
Hearing is a very important sense for detecting prey, avoiding predators, and staying alert to the surroundings. Snakes are vulnerable to predators such as monitor lizards, cats, dogs, and even other snakes. While they lack a middle and outer ear, they have a middle ear bone that connects the inner ear to the jaw. This enables the snakes to hear vibrations.
For their study, the researchers at Queensland University used a soundproof room to test a group of 19 snakes from seven species. They played one of three sounds, each including a range of frequencies: 1–150 Hz, 150–300 Hz and 300–450 Hz. To compare, the human voice range is about 100–250 Hz, and birds chirp at around 8,000 Hz.
Other researchers had previously hung western diamondback rattlesnakes (Crotalus atrox) in a steel mesh basket, observing their restricted behaviors in response to sound frequencies between 200Hz and 400Hz. Others had implanted electrodes into the brains of snakes, deselecting electrical potentials in response to sounds of 600Hz.
However, this is the first time a team investigates how multiple species of snakes respond to sound in a space in which they can move freely. The researchers also used an accelerometer to detect whether the sounds produced ground vibrations. This allowed them to confirm that snakes were registering airborne sounds and not just feeling vibrations.
The reaction depended on the type of snake. Woma Pythons (Aspidites ramsayi), a snake from Australia, increased its movement in response to sound and approached it. In contrast, three other types of snakes, Death Adders (Acanthophis), Taipans (Oxyuranus), and Brown Snakes (Pseudonaja), were more likely to move away from the sound.
“For example, woma pythons are large nocturnal snakes with fewer predators than smaller species and probably don’t need to be as cautious, so they tended to approach sound,” Zdenek said in a statement. “But taipans may have to worry about raptor predators and they also actively pursue their prey, so their senses seem to be much more sensitive.”
So, can snakes hear us? The frequency of the human voice is about 100 to 250 Hz, which is within their range -- but they can only hear us if we're loud enough. The sounds that the researchers played in their trials included these frequencies at 85 decibels – the amplitude of a loud voice. The snakes responded to this sound, which means it’s very likely that snakes can hear people speaking loudly or screaming.
The study was published in the journal PLOS ONE.