A tropical jumping spider needs ultraviolet wavelengths for courtship, say researchers.
The tiny spider, Cosmophasis umbratica, often turns up on sun-loving plants in tropical southeast Asia, explains Daiqin Li of the National University of Singapore. He and his colleagues knew that jumping spiders see ultraviolet (UV) wavelengths in sunlight, which people can’t. So, the team began checking for UV-reflecting markings on the spiders.
The team found that the male C. umbratica has patches on his face, legs, and underside that intensely reflect UV from sunlight. In courtship, he displays these patches for a female and vibrates his palps, appendages that stick out near his mouth.
The female of the species doesn’t have the same UV-reflecting patches, but her palps fluoresce when exposed to UV. That is, they absorb the energy of sunlight’s UV wavelengths and give off a greenish glow.
The researchers tested pairs of spiders, putting a male and a female in adjoining glass arenas. In full sunlight, males and females struck courtship poses. But when researchers blocked UV wavelengths from reaching one partner, the other rarely showed interest, the researchers report in the Jan. 26 Science.