A caterpillar turns into soup
A BUTTERFLY goes through four STAGES: EGG, LARVA, PUPA and ADULT. The larva, a caterpillar, does almost nothing but eat and GROW, shedding its skin several times. Then it hangs up and forms a CHRYSALIS, the pupa. Inside, most of the caterpillar's body breaks down into a kind of soup. Small clusters of cells that were there all along, waiting, use that soup to build a completely new body, with wings, legs, antennae and eyes. Moths do the same inside a silk COCOON.
Remarkably, some memories seem to survive the soup. In 2008 scientists trained caterpillars to avoid a particular smell, and the moths that emerged from the pupae still avoided it.
From frogspawn to frog
A frog lays its eggs in jelly-covered clumps of FROGSPAWN, while a toad lays hers in long strings. Each egg holds a tiny EMBRYO, and after a week or two a TADPOLE wriggles free. It breathes through gills, has a long tail and eats algae. Over the next few months it changes completely: back legs appear, then front legs, the gills are replaced by lungs, and the tail shrinks away as the body absorbs it for energy. The froglet climbs out of the water and becomes a MATURE frog, ready to REPRODUCE. Our pond life page covers the pond it grows up in.
Some insects skip the pupa. A grasshopper hatches as a NYMPH, a small wingless version of the adult, and grows by moulting several times.
Seeds that waited thousands of years
A SEED holds a baby plant and a store of food, and it can wait a very long time for the right moment to GERMINATE. In 2005 scientists in Israel planted a date palm seed found in the ruins of Masada, a fortress abandoned around 2,000 years ago, and it sprouted. The tree, nicknamed Methuselah, is still growing. In 2012 Russian scientists grew a small flowering plant from seeds that a ground squirrel had buried in the Siberian permafrost around 32,000 years earlier.
Once it has water, warmth and air, a seed swells, a root pushes down, a shoot pushes up to SPROUT, and the SEEDLING opens its first leaves to catch the light.
Animals that break the rules
The axolotl, a salamander from lakes near Mexico City, never really grows up. It keeps its feathery gills and lives in the water its whole life, still looking like a giant tadpole, and it can even regrow lost legs. A tiny jellyfish called Turritopsis goes further: when it is injured or starving, it can turn its adult body back into the young stage, a polyp stuck to the seabed, and start its life again. It has been nicknamed the immortal jellyfish, though in the sea most are eaten long before they get the chance.
Long waits and short lives
Some life cycles are remarkably lopsided. Periodical cicadas in North America spend thirteen or seventeen years underground as nymphs, then all emerge in the same few weeks, in their billions, to HATCH out of their skins, sing, mate and die. An adult mayfly may live less than a day; it cannot even eat. Every cycle ends the same way, with OFFSPRING starting the whole CYCLE again.