Teacher's Guide to the NOVA production: The Incredible Journey of Butterflies. The on-line video provides close-up video of the monarch's metamorphosis and migration to the mountains in Mexico. The video itself is directly embedded in the "Audio Visual for Students" tab.
Scientists have discovered that Monarch butterflies choose to feed on milkweed plants that have a specific chemical that makes the butterflies more toxic to its predators. Listen to a professional biologist explain the behaviors of Monarchs as related to their choice of medicinal plants.