The mystery of how butterflies with translucent wings stay dry has been solved by new high-resolution images – and the trick is bounciness.
Butterfly wings are covered in a dense array of microscopic overlapping scales that give them their remarkable colours and also repel water. But the wings of some species have transparent or translucent panels where there are far fewer scales, with large gaps between them. As well as helping the insects recognise other members of their species, the panels confuse predators that do not recognise the translucent zone as part of the butterfly. The price the butterflies pay is reduced waterproofing, but now ecologists at Kyoto University in Japan have discovered how they survive.
Pablo Goodwyn used electron microscopes to study the wings of the Japanese chestnut tiger butterfly, Parantica sita (pictured), which lives for up to six months and migrates up to 1000 kilometres. He found that scales shaped like flattened needles cover less than half of translucent areas. But because the scales tilt about 30 degrees upwards from the wing surface, they act like springs, bouncing away water droplets that land on them. A similar butterfly from the same area as P. sita does not have springy scales, so water can wet its wings. It lives less than a month (Naturwissenschaften, ).
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