Dare to get close enough to some sort of snake, you’ll quickly notice there’s no ear signal for you to whisper. Not a flap, flaw or groove to be seen. So you might be fooled into thinking they’re a little hard on the ears.
“Snakes are shy and very vulnerable creatures that hide most of the time, and we still have a lot to learn about them,” says toxinologist Christina Zdenek of the University of Queensland in Australia.
“Since snakes don’t have external ears, people often think they are deaf and can only feel vibrations in the ground and in their bodies.”
Although researchers have known for a long time that snakes are not deaf, their hearing is thought to be comparatively poor compared to their other senses such as taste and sight. For example, newborn pine snakes (Pituophis melanoleucus) are known to react more to visual than auditory stimuli, suggesting that their hearing is simply not up to par.
But there’s still some indication that hearing is important to the survival of many slitherers, potentially warning of approaching predators, for example.
Using 19 different types of snakes, including those that slither across the earth, sway in trees and slither in water, Zdenek and his colleagues tested sounds between 0 and 450 Hertz.
“We played a sound that produced vibrations in the ground, while the other two were just aerial,” explains Zdenek.
“This meant that we were able to test both types of ‘hearing’ – haptic hearing through the snakes’ belly scales and airborne hearing through their inner ear.”
Different groups of snakes responded to the sound of air differently, but those within the same genus responded similarly. This suggests that the responses are hereditary, the team explains.
“Only the woma python tended to move towards the sound, while taipans, brown snakes and especially death vipers were more likely to move away from it,” notes Zdenek.
Up to 2.7 meters and 5 kilos (8.9 feet and 11 pounds) tThe nocturnal woma python was the largest snake tested, with naturally fewer predators, so it makes sense that they are less cautious than the smaller species (40 grams to 2 kilograms) that are more active during the day. These pythons also hunt comparatively larger prey – monitor lizards. The smaller snakes, despite being some of the most venomous in the world, would be targeted by daytime predators such as birds of prey, monitor lizards and wildcats.
“Taipans may have to worry about predators of birds of prey, and they also actively pursue their prey, so their senses seem to be much more sensitive,” explains Zdenek.
This implies that the response to airborne sounds may be potential avoidance behavior, the researchers explain.
“We know very little about how most snake species navigate situations and landscapes around the world. But our study shows that sound can be an important part of their sensory repertoire,” concludes Zdenek.
This research was published in PLOS ONE.