The monarch butterfly, scientific name Danaus plexippus, is a large, orange-and-black butterfly, common to much of North America. It is famous for its annual migrations to and from wintering grounds in Mexico and California, see National Geographic, vol. 150, no. 2, August 1976.

The monarch starts life as an egg laid by the adult female on a leaf of the common milkweed plant, Asclepias syriaca. It is about the size of the head of a pin. When the egg hatches 3 to 12 days later, the tiny yellow-, white-, and black-striped worm-like larva, or caterpillar, has eight pairs of stubby legs for crawling about, and mouth parts designed for chewing leaves, which it does, voraciously. But only the leaves of the milkweed; no other plant will do. Now the milkweed has a white, sticky sap that is highly toxic to other animals, but does not affect the caterpillar at all, except to make his body, in turn, highly toxic to predators like birds that might like to eat the caterpillar for breakfast. And the birds, being no bird-brains, know to leave him alone….

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