Blue morpho: The rainforest butterfly that seems to glow

The blue morpho is the brightest star of the tropical rainforest: as it beats its wings it flashes a dazzling metallic blue. The most wonderful thing is that this blue is not a pigment — it is made by the tiniest structures on the wing surface. Let's see how it "glows".

Its body

The morpho's blue is called "structural colour": the scales on its wings carry a Christmas-tree-shaped nanostructure that reflects only blue light. So as you change your angle, the blue shifts; and if you wet it, the blue darkens for a moment. This flashing metallic blue makes it look like a stream of light as it flies, and predators find it hard to track.

The adult's mouthparts can only drink liquids, so its menu is fermenting fruit, tree sap and even the juices of carrion. Its caterpillars feed on legumes and wear fine hairs that can irritate the skin.

Where it lives and what it eats

The blue morpho lives in the dense rainforests of Central and South America. The adults use their flashes to communicate and court in the canopy and along the forest edge. Lovely as it is, it is a delicate animal that moves mainly by gliding and short wingbeats.

A note for grown-ups

You could talk with a child about having a colour without any pigment: imagine the butterfly's wing as a special mirror that reflects only blue. Children are often amazed that many beautiful colours in nature are, in a sense, an illusion our eyes create.