Ultraviolet (UV) reflective markings on male jumping spiders of the Cosmophasis umbratica species have been proven to impact the spiders’ sex recognition and sexual selection. A study led by Associate Professor Li Daiqin from National University of Singapore (NUS) Biological Sciences, has become the first to investigate the impact of two different types of UV on sexual signalling; UVA — UV light with wavelength between 315 and 400 nanometres, and UVB — UV light with wavelength between 218 and 315 nanometres.
“Only the male reflects UVA and UVB but the females don’t,” said Assoc Prof Li. “It’s a very important phenomenon called sexual dimorphism in colours.” The markings led the team to hypothesise that the males use the UV reflective markings to attract the females, while the markings on the males act as a factor for the females’ choice of mate and male-male competition.
These UV reflective markings are structure colours, Assoc Prof Li further explained. Unlike commonly used chemical colours like paint, the colours are not pigments but instead produced by the arrangement of physical structures like scales and feathers. They are seen as iridescence by human eyes and at different angles, can display different colours. This allows the spider to simultaneously camouflage itself and hide from predators while sending courtship signals. Studies into structure colours include biomimicry for use in the military industry.