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Summary
The U.S. Fish and Wildlife Service (FWS) has declared that one of North America's best known butterflies, the monarch, might be in trouble. But the agency put off protecting the insect under the federal Endangered Species Act, which may give researchers time to resolve a long-standing debate over how best to gauge the health of monarch populations. In recent months, dueling preprints and publications have intensified the debate. In one camp: researchers who have documented drastic declines in the number of monarchs in Mexico and other areas where some butterflies spend the winter. They believe the species needs even more immediate help, particularly by protecting and expanding the milkweed-filled meadows where its larvae feed. In another: scientists who have tallied the surveys of butterflies in areas they occupy during the warmer months and have concluded there is less cause for alarm.
