The Room 7 class, at Phillipstown School, asks :-

How do butterflies and moths get colours on their wings?

John Campbell, a physicist at the University of Canterbury, responded.

Some butterfly and moth wings are brightly coloured to advertise to predators that they taste terrible. Some tasty ones mimic the colours of the revolting tasting ones so fewer get eaten by predators. Some are coloured to camouflage themselves when resting on bark.

Hence the colours of moth and butterfly wings have evolved for many different purposes. In the same way, the methods by which these colours are produced are also varied. Some use chemistry, molecules that absorb some visible colours but not others. When white light falls on a red butterfly wing we see it as red because the green and blue light has been absorbed but the red is reflected.

When light falls on an array of straight lines it is diffracted. You can see this by looking at a distant street light through net curtains. You also see it on reflecting stickers which have areas of bright light whose colour changes as you rotate the sticker. These stickers are made from reflecting plastic film which has been stamped with straight lines very close together.

The wings of the morpho moth are covered with very tiny scales. These are covered by parallel ridges which are all equally spaced with about 2000 lines in each millimetre. Morpho moth wings were often included in victorian paintings because of their brilliantly iridescent blue colour.