The life of a butterfly begins as an egg, such as this one from a Monarch. It is hard to believe a caterpillar could emerge from such a small egg, it is only about 1 millimeter tall. Note the tiny lines radiating from the top of the egg. The mother monarch lays her eggs on only milkweed leaves (which she identifies by tasting them with her feet!), usually on the underneath side. A butterfly can lay over 500 eggs.