The monarch butterfly (Danaus plexippus), one of the most celebrated butterflies in the Americas, is known for its annual migration.
Each spring and fall they fly back and forth between the summer breeding grounds in the United States and Canada, and their winter resting grounds in Mexico.
Two distinct Monarch populations east and west of the Rocky Mountains are documented, with a population that winters in Southern California in areas such as Pismo Beach.
Field identification is usually easy. They have orange wings, outlined in black, and white spots on a black face.
Monarch butterflies made a good deal of news starting in 1999, when a researcher from Cornell University conducted a laboratory study on the effect of Bacillus thuringiensis (BT), a natural insecticide, on the monarch butterfly.
BT properties were being bred into some genetically altered corn varieties to deal with the European corn borer. Since milkweed and cornfields grow together, the fear was that monarch butterfly caterpillars were susceptible to harm, even to death, when they ingested milkweed leaves dusted with pollen from genetically engineered Bt corn.
The research brought on a wave of press attention questioning the safety of BT crops. Follow up research shows little harm to monarch populations to date.
