Kerry Thompson, age 10, of Winston Salem, North Carolina, for his question:

What exactly is a pupa?

It may look like a large brownish bean, dangling from a twig. Actually it is a living pupa and chances are it is a teenage butterfly. On some sunny afternoon, the pupa shell will crack open and a gorgeous butterfly will struggle forth, spread her wings and fly away. The pupa was once a hungry caterpillar and the caterpillar started life as an egg.

An insect of the butterfly clan goes through four stages of life. The third stage begins when the caterpillar stops eating and becomes a pupa, wrapped in a thin crisp shell. The pupa seems to be fast asleep, but actually it is very much alive. Inside the shell, the cells of the caterpillar's body become a soupy mishmash. Then the whole thing is remodeled to create a butterfly. This is the fourth stage of life and the insect is now a winged adult. When it hatches from the pupa, it flies off and lays eggs for the next butterfly generation.