Orb-weaving spiders use their web as an acoustic antenna

Hearing is a basic sense of many animals, including all mammals, birds, some reptiles, amphibians, fish, and arthropods. The hearing organs of these animals are extremely diverse in anatomy after hundreds of millions of years of evolution, but all of them consist of cellular tissue and are morphologically part of the animal body. New research shows that hearing in a species of orb-weaving spider called the spider bridge (Larinioides sclopetarius) is not limited by the body of the organism but is expanded by the externalization of hearing to its self-made protein orbital web.

A spider’s web is a huge reconfigurable, regenerative and very sensitive acoustic antenna. Image credit: Zhou et al., doi: 10.1073/pnas.2122789119.

A single strand of spider silk is so fine and sensitive that it can detect the movement of the vibrating air particles that make up a sound wave.

This is different from the functioning of the eardrums, by sensing the pressure of sound waves; spider silk detects sound from nanoscale air particles that are excited by sound waves.

“The individual strands of silk are so fine that they essentially float with the air itself, jostled around by local air molecules,” said Professor Ron Hoyresearcher in the Department of Neurobiology and Behavior at Cornell University.

“Spiders can detect tiny movements and vibrations via sensory organs in their tarsi – claws at the end of their legs that they use to grasp their webs.”

Orb weaver spiders are known to make large webs, creating a kind of acoustic antennae with a sound-sensitive surface that is up to 10,000 times greater than that of the spider itself.

In the study, Professor Hoy and his colleagues used a special quiet room with no vibrations or airflow.

They had an orb-weaver build a web inside a rectangular frame, so they could position it wherever they wanted.

The researchers started by placing a mini-speaker a few millimeters from the canvas without actually touching it, where the sound works like a mechanical vibration.

They discovered that the spider sensed the mechanical vibration and moved in response.

They then placed a large loudspeaker 3m on the other side of the frame piece with the web and spider, beyond the range where mechanical vibrations could affect the web. A laser vibrometer was able to show the vibrations of the tape from excited air particles.

The authors then placed the speaker in different locations, right, left, and center relative to the frame.

They discovered that the spider not only detected sound, it rotated in the direction of the speaker when moved. Also, it behaved differently depending on the volume, when crouching or when flattening.

“This finding opens up new insights into extended animal cognition and hearing – the externalization and oversizing of auditory function in spiders,” they said.

“The study calls for reexamining the remarkable evolutionary and sensory ecology of spiders – one of the oldest land animals.”

“The sensory modality of externalized hearing provides a unique model for studying extended and regenerative sensing and presents novel design features to inspire novel acoustic flow detectors.”

the results appear in the Proceedings of the National Academy of Sciences.

_____

Jian Zhou et al. 2022. Externalized hearing in an orb-weaving spider that uses its web as an auditory sensor. PNAS 119 (14): e2122789119; doi: 10.1073/pnas.2122789119

Comments are closed.