The ogre-faced spiders, named for their huge eyes, add to their incredible night vision already known the listend capacity to their predators and prey, according to a new study.
Having no ears, these spiders use hairs and joint receptors on their legs to pick up sounds dis at least 2 meters away. The results, published in Current Biology, suggest that spiders can hear low-frequency sounds from prey such as insects, as well as high-frequency sounds from their predators, birds.
“I think a lot of spiders can hear, but everyone takes it for granted that spiders have a sticky web to catch their prey, so just are good at detecting nearby vibrations“says lead author Ron Hoy, professor of neurobiology and behavior at Cornell University.” Vibration detection works to detect cobweb or ground shaking, but detecting those disturbances in the air at a distance is the responsibility of the hearing, which is what we and spiders do too, but they do it with specialized receptors, not with eardrums. ”
Rather than passively waiting for prey to fall into a web and get stuck, ogre-faced spiders they use their nets as a weapon. After spending the day hours completely still, mingling with the surrounding palmetto leaves, they emerge at night to hang close to the ground and cast their nets like a net over unsuspecting insects. While they use their keen night vision to catch prey on the ground, they can also catch insects in midair by performing an elaborate choreographed backswing, which does not appear to rely on vision.
“In a previous study, I actually put dental silicone over their eyes so they couldn’t see,” says first author Jay Stafstrom, a postdoctoral researcher at Hoy Lab. “And I found that when I returned them to the wild, they couldn’t catch prey from the ground, but they could catch insects from the air. So I was pretty sure that these spiders were using a different sensory system to hunt down flying insects. ”
While that study hinted that spiders could hear, it showed how well they can. By observing the spiders ‘reactions to different tones and measuring their neural response with electrodes placed on the spiders’ brains and legs, the team determined that the spiders could hear sounds up to 10 kHz in frequency, much louder than the sounds of a flying or terrestrial insect.
“When I was playing low pitched frequencies, even from a distance, they hit like they were hunting an insect, which they don’t do with higher frequencies,” says Stafstrom. “And the fact that we were able to do that from a distance, knowing we’re not getting close and making them vibrate. That was key to knowing that they can really listen. ”
Hearing these higher frequencies may not be helpful for hunting, but it can help them stay alert when hiding from their own predators.
While these results make it clear that spiders can detect sounds well, the researchers are interested in test your directional hearing, if they can tell where the sounds are coming from. If they can also hear directionally, this might help better explain their acrobatic hunting style.
“What I found really amazing is that to throw their net at the flying insects they have to do a half backflip and extend their net at the same time, so they’re essentially playing center field,” Hoy says. “Directional hearing is a big problem in any animal, but I think there will really be some interesting surprises from this spider.”