Spider Seduction Requires UV Light

When some spiders desire a little romance in their lives, they use ultraviolet light as the aphrodisiac. Biologists in Singapore and England have now added the ornate jumping spider Cosmophasis umbratica to a growing list of critters—including parrots, butterflies, and fish—that rely on UV reflection and fluorescence to socialize (Science 2007, 315, 481).

What makes these spiders' use of UV light stand out—besides the afterglow—is that UV reflectance and UV-induced fluorescence are employed on a sex-specific basis. Without UV wavelengths, these spiders get no love.

Males reflect UV light off scales on their faces and bodies during the mating game, whereas females have sensory organs called palps, typically used to capture prey, that fluoresce bright green when excited by UV light.

In the absence of UV light, the success rate for consummating courtships decreases, explains senior author Daiqin Li of the National University of Singapore. Although he suspected the jumping spider might use UV reflectance to communicate, the discovery of female fluorescence came as a total surprise.

"The fluorescence really seems absolutely essential for the males to recognize the females," comments Thomas Cronin, who studies fluorescent shrimp at the University of Maryland, Baltimore County. "In most other creatures, fluorescence is a supplementary signal to add contrast. In these spiders, it seems necessary for the male spider to find a female." The proteins responsible for reflecting UV light in the males and triggering UV-induced fluorescence in the females have not yet been identified, but Li's group is looking for them.

Li suggests that the nanostructures the male spiders use to reflect UV light could have many applications, not only in biomedical sciences and ophthalmology but also in automobile and textile industries, energy storage, and laser optics.

As the list of critters that capitalize on UV optics to enhance their communication gets longer, "about the only animal group for which UV seems not so important is mammals, making us the exception," comments Justin Marshall, a biologist at the University of Queensland, in Brisbane, Australia. But humans compensate, he says, with whiter-than-white laundry detergent, bright and bold Post-it notes, and glow-in-the-dark tattoos for nightclubbing.