Many spider species rely heavily on vibrations to send signals to one another, by shaking leaves or strands of their webs. Often referred to as thrumming, the behavior produces a steady rhythmic vibration.

However, one type of wolf spider (Gladicosa gulosa) goes beyond mere thrumming - it purrs like a cat. The males rub together appendages (called pedipalps) near their mouth to make vibrations, which is their way of communicating with females. The sound produced is loud enough to be heard by human ears a meter (39”) away.

However, female spiders, unlike humans, don’t have ears; they must detect the vibrations of the male’s courtship signals through a surface such as dried leaves. The males only produce the sounds if they are standing on something that will vibrate, like a leaf, and females only respond when perched on a similar surface.

Scientists theorize that the male’s signal may reach the female by travelling as sound in air, which causes the leaves the female is standing on, to vibrate. “We think that’s how she ‘hears’ the sound,” says one researcher. “Spiders have very sensitive structures all over their bodies for detecting vibration, even at low levels, so we’re working on the hypothesis that they detect a surface vibration induced by an airborne sound.”

The sound produced has also been compared to a wad of money being quietly thumbed, so perhaps the males are onto something.

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