Driven by the forces of sexual selection, male--and, in some instances, female--animals have evolved a dizzying array of mating displays and rituals.
For jumping spiders, mating can be an tricky affair--but not for the reasons you might think. According to a recent study published in Current Biology, jumping spiders communicate during courtship using ultraviolet B (UVB) light, which humans are unable to see. While scientists have long known that certain species use UVA light for communication, this was the first study to demonstrate that some are also able to detect shorter-wavelength UVB light.
The male jumping spiders have specialized scales that glow white and green when exposed to UV light; in female spiders, the palps (front appendages) appeared green under UV light. And the absence of UVB light effectively killed the mood: As soon as either sex was exposed to light without ultraviolet rays (and the showy scales or palps were obscured), the other immediately lost interest in mating.
This image shows a female jumping spider's palps under normal lighting.