Every fall, spectacular orange and black clouds of monarch butterflies fill the skies as they migrate from across North America to Central Mexico. West Coast populations make a similar though much shorter trip to coastal California. The National Wildlife Federation calls the monarch migration -one of the greatest natural phenomena in the insect world.- Not long ago, monarchs numbered in the billions, but in the last 20 years their population has dropped by 90%, due to habitat loss from pesticides, modern farming practices, urban development and other human activity. An estimated one...