Have you seen them? They're baaa-aack! It always warms my heart a bit when I go outside to look at my milkweed and find monarch caterpillars or their chrysalis dangling on the branches.
Monarch caterpillars are pretty distinct. Obviously, they are a caterpillar, so they have a worm-like body that is yellow, white and black striped. The caterpillars have two long, black projections that look similar to antennae towards the head region and then two black shorter projections near the end of the abdomen.
The pupa, or chrysalis, is usually formed on the milkweed plant and starts off bright green with metallic gold at the top. The chrysalis will change colors as time goes on and the caterpillar transforms into a butterfly. It eventually becomes transparent and you can kind-of see the butterfly inside.
After the adult (the butterfly) emerges from the chrysalis, it spreads it's wings and stays in place for several hours to allow it's exoskeleton to dry and harden before it can fly away.