Spiders might have ears everywhere according to new research that is reimagining their webs as “external eardrums”. In it, the authors demonstrate how the orb-weaving spider, Larinioides sclopetarius, might outsource sound perception to a structure outside of its body.
According to the preprint paper, which is not yet peer-reviewed but available to read on BioRxiv, the wispy nature of orb weavers’ webs not only acts as an acoustic “antenna” for detecting sound but is actually one of the most effective “eardrums” in nature.
A nifty piece of kit called the tympanic eardrum emerged in the evolution of terrestrial species as they needed to listen out for subtle, airborne sounds. Most humans have one in each ear and it separates the outer from the inner ear, and if it gets damaged it can greatly impact hearing.
For invertebrates without this kit in their bodies, long spindly structures sprouted that were able to detect airborne sounds. Whatever the solution, these sound organs all formed a part of the animals’ bodies.
This new research looked at the webs of L. sclopetarius that were spontaneously spun by lab animals inside wooden frames. The researchers then videotaped them to see if or how the spiders responded to airborne acoustic tones coming from different distances and directions.
Their recordings showed that the spiders' body posture changed even in response to relatively distant sound emitted from 3 meters (10 feet) away from the web. They would crouch, flatten their bodies, display with their forelegs, and change direction abruptly in response to the sounds.
The researchers say that the spiders’ potential predators and prey such as birds, frogs, and crickets get pretty loud (> 80 dB), but their lab experiments showed the spiders to have a hearing threshold lower than 68 dB. With this in mind, they predict these spiders should be able to detect predators and prey at a distance more than 10 meters (32 feet) away.
The preprint paper is yet to undergo peer review, but should the result be found to hold it could indicate that spiders have managed to overcome body size constraints to create an external eardrum that can be up to 10,000 times the surface area of the spider itself. It wouldn't be the first account of spider hearing, with ogre-faced spiders thought to "hear" with their hairy legs.
Beyond enormous size, the perks of hearing with sustainable and repairable spider silk means that spiders could adjust their giant, acoustic antenna landing pads according to their needs. An enviable trait for anyone who’s ever suffered through the frustrating recovery period of a perforated eardrum.
“Biologists and material scientists are still discovering new properties of spider silk that can be repurposed as a biomaterial and deployed for practical human applications,” say the researchers in their paper.
“The “outsourcing” and “supersizing” of auditory function in spiders provides unique features for studying extended and regenerative sensing and designing novel acoustic flow detectors for precise fluid dynamic measurement and manipulation.”
[H/T: New Scientist]
