Ultraviolet reflection and predation risk in diurnal and nocturnal Lepidoptera

According to our extensive data on Lepidoptera (883 species), UV wing patterns are almost three times more common in nocturnal than in diurnal Lepidoptera. This might be due to predation, because the primary diurnal predators, birds, utilize UV light in foraging and even prefer UV-reflecting prey. To test this hypothesis, we conducted a field experiment with tethered living moths whose wings were artificially manipulated to reflect (UVþ, reflection at UV wavelength: 15%) or absorb (UV ) UV light, keeping longer wavelengths identical. Thus, any difference found in survival rates would be the result of the difference in wing patterns in UV spectrum. Significantly more UVþ moths than UV ones were eaten in the daytime, but no difference in predation rates could be detected when moths were exposed to nocturnal predators. The different survival rates indicate that UV reflection increased predation risk by visually orienting diurnal predators. The lack of difference at night arises from the lack of UV-sensitive predators. UV wing patterns, even if they are important in intraspecies communication, seem to be costly to diurnal Lepidoptera by attracting predators.