UV light may be invisible to us but many animals can see it and use it to communicate. Sometimes, this is deliberate, as in the case of blue tits using UV patches to seduce females. It can also be inadvertent and downright unfortunate, as in the case of voles that give away their position to hovering kestrels through the UV reflections from their urine. Even though UV-based messages are widespread, those of the jumping spiders are unique, for they use a specific type of ultraviolet light called UVB.

The UV-sensitive cells in animals that can detect ultraviolet light almost always respond most strongly to UVA, the type that lies closest to violet and has the longest wavelengths. It’s usually been