Image Credit: Mike Keeling via Flickr // CC BY-ND 2.0
Go ahead and add purring to your list of normal spider behavior: The wolf spider Gladicosa gulosa communicates with potential mates through purr-like sounds, according to a study in the Journal of the Acoustical Society of America.
It’s not quite a purr on the level of Merlin the cat, but the spider’s love song is audible. (You can listen to them here.) Most spiders don’t make noises, and they don’t have ears—they communicate through vibrations. While sound is physically a vibration, acoustic communication is a different biological process than vibration, and spiders don’t have the physiological underpinnings for it.
So, in order to vocalize their proclamations of sexual interest, spiders use the world around them. The male wolf spider stands on a thin surface, like a dead leaf, and vibrates it until it makes a sound. The female, in turn, responds to the calls when they’re on a similar surface, which picks up the vibration. In the study, female spiders still responded to acoustic male mating calls even when the spiders were not on a vibrating surface.
It’s likely a system built on talking specifically to the ladies. It’s not the most sophisticated sense of hearing, but it will get the job done. If only that job wasn't making legions of terrifying spider babies.