Researchers have discovered that all kinds of animals -- from sea slugs and caterpillars to songbirds and people -- undergo constant and remarkable physical changes during their lives.

Many animals have a special ability to transform themselves, for the sake of survival, reproduction, or both.

Imagine being eaten alive -- from the inside out! That is what happens to any caterpillar unlucky enough to become the nest for an egg laid by a caterpillar wasp.