Spiders are sensitive to airborne vibrations from nearby sources. They are supposed to respond to sounds and ‘hear,’ but only when the sound is coming from a few inches away. Now, a Cornell University-led research team has found that jumping spiders, and most likely other spiders too, can hear sounds over much greater distances.
A daring jumping spider (Phidippus audax), an adult female. Image credit: Ryan Kaldari.
“The sensory world of the tiny jumping spider was thought to be dominated by sight and tactile touch. Surprisingly, we found that they also possess an acute sense of hearing,” said lead author Paul Shamble, a former graduate student in the Department of Neurobiology and Behavior at Cornell University and now a researcher at the Hebrew University of Jerusalem.
“They can hear sounds at distances much farther away than previously thought, even though they lack ears with the eardrums typical of most animals with long-distance hearing.”
Behavioral experiments by the team with the daring jumping spider (Phidippus audax), a common jumping spider of North America, revealed that these animals respond to low-frequency sounds by freezing — a common anti-predatory behavior.
“Neurophysiological recordings from auditory-sensitive neural units in the brains of these jumping spiders showed responses to low-frequency tones — recordings that also represent the first record of acoustically responsive neural units in the jumping spider brain,” the authors explained.
“Responses persisted even when the distances between spider and stimulus source exceeded 10 feet (3 m) and under anechoic conditions.”
“Thus, these spiders appear able to detect airborne sound at distances in the acoustic far-field region, beyond the near-field range often thought to bound acoustic perception in arthropods that lack tympanic ears.”
The scientists also found that direct mechanical stimulation of hairs on the spiders’ forelegs was enough to generate a response in acoustically sensitive neurons.
“We found that when we shook single sensory hairs back and forth — these are the same hairs that are known to respond to sounds originating close to the animal — we also got responses,” Dr. Shamble said.
“This suggests that these hairs are how spiders are registering far-away sounds.”
Further experiments showed that the jumping spiders’ hearing is most sensitive to frequencies that would enable them to hear the wingbeats of their parasitoid wasp enemies.
The team’s findings were published online October 13 in the journal Current Biology.
The authors are now recording from the brains of fishing spiders and wolf spiders, among several other more interesting members of this large and diverse group of invertebrates, to test their hearing too.
_____
Paul S. Shamble et al. Airborne Acoustic Perception by a Jumping Spider. Current Biology, published online October 13, 2016; doi: 10.1016/j.cub.2016.08.041
