Ability to see UV light helps birds and bugs survive, photos suggest

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ABIKO, Chiba Prefecture–Some species of birds and bugs are seeing the world in a different light from humans.

Ultraviolet light, not visible to humans through the naked eye, enables crows, butterflies and other species to distinguish friend from foe, images shot by a retired high school teacher here suggest.

Using a customized camera designed to capture ultraviolet rays, Shigeru Asama, 69, photographed various species in Japan and abroad.

Photos he took on his travels from Hokkaido to Okinawa and over to Borneo appear in his book “Mushi ya Tori ga Miteiru Sekai” (The world bugs and birds see), published this spring by Chuokoron-Shinsha Inc.

The wings of the male cabbage butterfly appear darker through the camera because they suck up ultraviolet rays. The wings of females look bright because they reflect ultraviolet rays.

The findings indicate that it’s no problem for the butterflies to tell males from females although it’s a challenge for humans.

To the human eye, jungle crows are completely black. But Asama’s ultraviolet images showed that each bird has its own unique pattern, leading him to conclude that the species can identify individual crows based on the pattern.

“The ultraviolet photos provide clues to survival strategies of animals,” Asama said.

Lizards that share their habitats with snakes, their predators, tend to have tails that reflect ultraviolet rays more, the photos revealed.

Asama said that can be a lifesaver for lizards as the light acts as a distraction when they shed their tails to escape predators.

Other predators use ultraviolet light to their advantage.

A carnivorous plant of a nepenthes variety appears to lure insects with its traps that reflect ultraviolet light, Asama said.

Gen Morimoto, 44, a researcher at the Yamashina Institute for Ornithology here, welcomed Asama’s findings.

“Although the book includes some hypotheses that have not been verified sufficiently, it has shed a valuable light on the connection between living creatures’ appearance and ecologies from the perspective of ultraviolet rays,” Morimoto said.

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