Animals are involved with eating and sex. Some insects split up the roles to different phases of their lives. After butterflies hatch, they become small caterpillars, and focus only on eating. No sex. After they grow large enough, they enter the cocoon stage, and emerge as butterflies. Now the focus is only on sex and not food. They fly around looking for mates. They do not last too long, as they do not eat. This dual strategy seems to work!