Wolf spiders are deaf — they don't have the right structures for hearing. However, they are very good at sensing other kinds of vibrations, and they use this ability to communicate. One species of wolf spider plays songs on dead leaves to attract mates.
To woo a lady spider, the male wolf spider stands on a dead leaf and bounces or taps his legs to vibrate the leaf. It's a very small vibration, not enough to make a sound that you could hear, but it travels through leaves so well that another spider standing on a nearby leaf can feel it. It's a silent signalling system that helps lonely wolf spiders pair up. Like arachnid Tinder.
For one species, though, it's not actually silent, according to recent research by biologists at the University of Cincinnati. The purring wolf spider, known more formally as Gladicosa gulosa, bounces on leaves to create the same silent vibrations as its cousins, but it also makes an audible sound. It's very quiet, and you still probably wouldn't hear it amid the other noises of the forest, but you can listen here.
The biologists, Alexander L. Sweger and George W. Uetz, weren't sure whether making an audible sound helped male purring wolf spiders reach out to female spiders, though, since they can't actually hear the sounds. But they discovered that the audible sound could still travel through the air to another leaf, where it would create the same non-acoustic vibrations that a female spider can feel.
One question remains: If a spider vibrates a leaf in the forest, will he get a date?
Image: AceSmythe via Wikimedia Commons