As a butterfly caterpillar grows it must molt its skin. Each stage between molts is called an instar. All five instars of the Monarch are shown in the caterpillar photo. The chrysalis, or pupal skin, of the Monarch is strikingly beautiful. In the final day or two before emergence, the chrysalis becomes transparent, allowing one to see the orange and black wings beneath.
Some butterflies are very specific about where they lay their eggs.
Monarchs will only lay their eggs on milkweeds. Milkweeds contain a potent heart poison, which helps to protect them from browsing animals and leaf-eating insects such grasshoppers. Monarchs are able to store this poison within their own bodies, making themselves poisonous in turn. They are very brightly colored, both as a caterpillar and as an adult, to advertise that they are not good to eat. Whenever an insect is brightly colored, rather than camouflaged to match its background, it usually means they have a secret weapon.