This photo shows a frontal view of an ogre-faced spider with large eyes. Photo credit: Jay Stafstrom
Ogre-faced spiders, named for their massive eyes, hide during the day and hunt at night, dangling from palm fronds in Florida and throwing silk webs at insects on the ground and in the air. In addition to their incredible night vision, these spiders can also hear their predators and prey, researchers report in the Journal Current biology on October 29, 2020. Since the spiders don’t have ears, they use hair and joint receptors on their legs to pick up sounds from at least 2 meters away. The results suggest that spiders can hear low-frequency sounds from insect prey as well as higher-frequency sounds from bird robbers.
“I think a lot of spiders can actually hear, but everyone takes it for granted that spiders have a sticky web to trap prey so they’re only good at detecting tight vibrations,” says senior author Ron Hoy , Professor of Neurobiology and Behavior at Cornell University. “Vibration detection is used to detect shaking of the web or the ground, but recognizing these disturbances in the air from a distance is the province of hearing. We do that and so do the spiders, but they do this with special receptors, not with eardrums . ”
This high-speed video shows an ogre-faced spider striking backwards. Photo credit: Sam Whitehead
Instead of passively waiting for prey to fall into a web and get stuck, ogre-faced spiders use their webs as weapons. After spending the day in complete silence and interfering with the surrounding palmetto fronds, they emerge at night, dangling close to the ground and throwing their nets like a net at careless insects. While using their keen night vision to catch prey on the ground, they can also catch insects in the air by performing an elaborately choreographed backward strike that does not appear to be based on sight.
“In a previous study, I actually put dental silicone over their eyes so they couldn’t see,” says lead author Jay Stafstrom, a postdoctoral fellow at the Hoy Lab. “And I found that when I brought them back into nature they couldn’t catch prey from the ground, but they could still catch insects from the air. I was pretty sure these spiders were using a different sensory system to hunt down flying insects. ”
This photograph shows the wrong posture taken by ogre-faced spiders while waiting for prey to be handed over. Photo credit: Jay Stafstrom
While this study indicated that the spiders might be able to hear, this one showed how well they can. By observing the spiders ‘responses to various sounds and measuring their neural response with electrodes in the spiders’ brain and legs, the team found that the spiders could hear sounds at frequencies up to 10 kHz, which were far higher than that Sounds of walking or flying insect.
“If I played low audio frequencies from a distance, they would strike as if they were chasing an insect, which they don’t do for higher frequencies,” says Stafstrom. “And the fact that we did it remotely because we know we’re not going to get up close and make it vibrate. That was the key to knowing that they could really hear. ”
Hearing these higher frequencies might not be helpful for hunting, but it can help them stay vigilant when hiding from their own predators.
“If you give an animal a threatening stimulus, we all know about the fight or flight response. Invertebrates have that too, but the other ‘f’ is ‘freeze’. That’s what these spiders do, ”says Hoy. “You are in a cryptic attitude. Your nervous system is asleep. But as soon as they perceive some sort of salient stimulus, boom, that turns on the neuromuscular system. It is a selective attention system. ”
While these results make it clear that the spiders can recognize sounds well, the researchers are next interested in testing their directional hearing – whether they can tell where sounds are coming from. If they can also hear directly, this can help further explain their acrobatic hunting style.
“What I found really amazing is that they have to do a half back flip while also spreading their web to throw their net at flying bugs so they are essentially playing in midfield,” says Hoy. “Directional hearing is a big deal with any animal, but I think there are really going to be some interesting surprises from this spider.”
Reference: “Ogre-faced, web-cast spiders use acoustic signals to detect prey in the air” by Jay A. Stafstrom, Gil Menda, Eyal I. Nitzany, Eileen A. Hebets and Ronald R. Hoy, October 29, 2020, Current biology.
DOI: 10.1016 / j.cub.2020.09.048
This work was supported by the National Science Foundation
