Moths use colour to see flowers at night

A NOCTURNAL moth has become the first animal known to see colours in the dead of night. They use this visual talent to find yellow, nectar-packed flowers in the dark, but the finding reported in New Scientist suggests that other species also use colour vision at night.

Nocturnal moths were thought to find flowers by looking for bright petals against a darker, leafy background.

To test this idea, researchers at Lund University in Sweden trained nocturnal elephant hawkmoths (Deilephila elpenor) to pick out yellow or blue artificial flowers from eight other flowers of varying shades of grey. They then made moths perform the trick in conditions as dark as a starry but moonless night.

The insects picked the correct flower 90 per cent of the time. But the moths could not distinguish between lighter and darker shades of a coloured flower, even though they could still tell both from grey. Almut Kelber, the sensory biologist leading the Lund team says they could only have used the spectral composition of the signals — which we call colour.

The moths use three separate colour receptors: blue, green and ultraviolet. At night, that leaves so little light per receptor that the insects should be almost blind.

But hawkmoths have a host of adaptations to compensate. One is a mirror-like structure at the base of the eye, which reflects light across the photoreceptors for a second time. The structure of the compound eye also allows each facet to supplement the light that strikes it with light from as many as 600 others.