Complex sentence: The black or red caterpillars feed on certain compatible "Aristolochia" species, making them poisonous as both larvae and adults, while the adults feed on the nectar of a variety of flowers.
Split into simpler sentences: The black or red caterpillars feed on certain compatible "Aristolochia" species, making them poisonous as both larvae and adults. The adults feed on the nectar of a variety of flowers.