Some animals are primarily visual, making sense of the world as a blend of color and light. Others have a keen sense of smell, and track prey for miles and miles with only olfactory clues to guide them. But certain species of spiders take the cake for "strangest method of information-gathering:" through sensing vibrations in their webs, they can tell what sort of prey has been captured, whether certain patches of the web need to be repaired, and even when a hot date is advertising!
These spiders have highly sensitive vibration-sensing organs called slit sensillae on their legs. The spider can pluck web strands (like a musician strumming a guitar) then listen for echoes that might indicate structural weakness. By "tuning" the silk, the spider strengthens its web.
Researchers discovered this amazing ability through a combination of high-speed video and laser measurements. Of course, spiders don't need any equipment beyond what they are born with! This is reminiscent of a memorable passage from E.B. White's Charlotte's Web:
“Do you understand how there could be any writing in a spider's web?"
"Oh, no," said Dr. Dorian. "I don't understand it. But for that matter I don't understand how a spider learned to spin a web in the first place. When the words appeared, everyone said they were a miracle. But nobody pointed out that the web itself is a miracle."
"What's miraculous about a spider's web?" said Mrs. Arable. "I don't see why you say a web is a miracle-it's just a web."
"Ever try to spin one?" asked Dr. Dorian.”
Dr. Dorian was right-- researchers are only just discovering the amazing properties of spider silk, and have been trying for years to replicate silk in a manner useful for human engineering. We have good reason to do so: it is stronger on a per-weight basis than steel!
"By plucking the silk like a guitar string and listening to the 'echoes' the spider can also assess the condition of its web," Mortimer said. If there's a problem, the spider can "tune" the silk, adjusting its properties, tensions and how it interconnects with other areas.