The ogre-faced spider has a trick up its sleeve, or should I say “legs”? These receptive arachnids, so named for their massive eyes, are proficient hunters thanks to their big googlies, but amazingly they can also hear. This might perplex those who are aware spiders don’t have ears, but new research published in the journal Current Biology has discovered that ogres can use their hairy legs to detect low- and high-frequency sounds from prey and predators.
Ogres are active hunters and use their webs like weapons rather than hanging about waiting for a fly to drop in. They catch passing insects by hanging while holding a collection of silk, trapping them as they go by a bit like casting a net. Their eyes help them to wrangle insects on the ground, but this new research shows it's their legs that enable them to detect flying prey.
To establish the ogres weren’t using their eyes to do this, the first author on the study Jay Stafstrom from the Hoy Lab at Cornell University used dental silicone to cover the eyes of this big spider. When he set them loose to catch some bugs, the spiders stopped hunting for ground-dwelling insects and instead stuck to catching insects in the air, indicating they were using something other than their eyes to hunt in this way.
Stafstrom and colleagues wanted to investigate the observation further and monitored the reactions of ogres to different tones. They did this by attaching electrodes to the spiders’ brains and legs and were able to determine that the spiders could hear anything up to 10 kHz. Whether this ability to hear is most useful for hunting or for keeping an ear (read: leg) out for predators isn’t yet clear, but their response to noises appears to imply the latter.
"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," said Ron Hoy, a professor of neurobiology and behavior at Cornell University, in a statement. "They're in a cryptic posture. Their nervous system is in a sleep state. But as soon as they pick up any kind of salient stimulus, boom, that turns on the neuromuscular system. It's a selective attention system."
The team’s next move is to investigate how good ogres are at interpreting where a sound is coming from, as this kind of directional hearing may provide insights into their unusual and acrobatic hunting style.
"What I found really amazing is that to cast their net at flying bugs they have to do a half backflip and spread their web at the same time, so they're essentially playing centerfield," said Hoy. "Directional hearing is a big deal in any animal, but I think there are really going to be some interesting surprises from this spider."
If you think hearing with your legs is weird, wait until you find out which animal uses its arms to taste.