Life cycle of a butterfly

A butterfly does not grow up the way you do. It takes its own body apart and builds a new one, and it wears four completely different bodies in a single lifetime. Watch the loop go round.

Egg

A monarch egg is the size of a pinhead, glued one at a time to the underside of a milkweed leaf. The mother tastes the leaf with her feet first, to be certain her caterpillars will hatch onto the only plant they can eat.

Newly hatched caterpillar

After three to five days a caterpillar chews its way out, and its very first meal is its own eggshell, which is packed with protein. Then it starts on the leaf itself, and from here it barely stops eating at all.

Moulting

A caterpillar's skin cannot stretch. When it gets tight, the caterpillar grows a roomier one underneath, splits the old skin down the back and walks straight out of it, usually leaving the old face mask stuck to the leaf.

Growing caterpillar

Between moults it eats around the clock. A monarch caterpillar hatches weighing about half a milligram and ends up roughly two thousand times heavier by the time it stops, which is like a newborn baby growing to the weight of a bus.

Fully grown caterpillar

By the fifth and final skin the caterpillar is around five centimetres long and boldly striped. Milkweed sap is poisonous, and the caterpillar stores that poison inside its own body, so a bird that tries one gets sick and never forgets those stripes.

Hanging in a J shape

It stops eating and wanders, sometimes for hours, hunting for a safe branch. Then it spins a small button of silk, grips it with tiny hooks on its back end and hangs upside down in the shape of the letter J.

Chrysalis

The skin splits one last time and underneath is the chrysalis, jade green with a line of gold dots. This is not a cocoon and there is no silk wrapping. A chrysalis is the insect's own skin, hardened into a case.

Metamorphosis inside

Inside, almost the entire caterpillar dissolves into a thick soup. Small discs of cells that have been carried since the egg use that soup as raw material and build wings, legs and eyes from scratch. It takes about ten days.

Emerging adult

The case turns clear and you can see folded orange wings through the wall. The butterfly cracks it open and hauls itself out with a swollen body and crumpled wet wings that look far too small ever to work.

Pumping up the wings

It pumps fluid from that fat body out into the wing veins, inflating them like a balloon, then hangs perfectly still for two or three hours while they harden. A butterfly knocked down at this moment sets crooked and never flies.

Adult butterfly

The adult will never grow another millimetre. Every butterfly you meet is already full size, so a small one is not a baby, it is simply a smaller species. Its wings are roofed with overlapping scales, like tiles on a house.

Feeding on nectar

It has no jaws at all any more. It drinks through a coiled straw called a proboscis, and it tastes with its feet, which can find sugar in a solution far too weak for your tongue to notice.

Mating and laying eggs

Most adults live only two to six weeks, just long enough to find a mate and lay eggs. A female lays a few hundred, one at a time, on fresh leaves, and the whole four bodied journey begins all over again.