We live in Santa Cruz, California, one of the areas where the Monarch butterflies gather after their migration, and we regularly see Monarchs in our garden. Their populations have been declining drastically. Scientists have said that planting milkweed would help, since Monarchs require milkweed for their life cycle. They lay their eggs on the milkweed and the young feed on the toxic plant, making the caterpillars undesirable to birds other prey. Planting milkweed also provides flowers for bees and other butterflies as well. So we added some milkweed to the garden this year.