One monarch caterpillar on a common milkweed plant.
Please keep planting and encouraging those milkweeds. Unlike Brian Wildsmith's caterpillar who ate just about everything, monarch caterpillars just eat leaves from plants of milkweed species. Monarch butterflies eat the nectar of milkweed and other plants, but only lay eggs on milkweed. The United States Fish and Wildlife Service estimates that 1.8 billion more milkweed plants could save the eastern population of monarch butterflies, and 30% of the additional milkweed plants could be grown in cities--private yards and public spaces.