Half of Monarch Butterflies Migrate From Upper Midwest, Scientists Find

Half the monarch butterflies wintering in Mexico come from a relatively compact region of the upper Midwest, according to scientists who say conservation efforts should be targeted there. More than 100 million of the colorful monarchs migrate south each year to spend the winter in Mexico.

Wintering sites in Mexico are threatened, but the Canadian scientists who discovered the Midwestern origin of the butterflies report in the Proceedings of the National Academy of Sciences that the breeding areas are at even greater risk because of intensive farming and pesticide use. Farming is destroying milkweeds, which are the primary food for butterfly larvae.

Compiled by Times medical writer Thomas H. Maugh II