Monarch butterfly migration in North America: Controversy and conservation.

The monarch butterfly is the most spectacular example of insect migration known. Monarchs are threatened by the destruction of their over-wintering sites in Mexico, California and elsewhere, and many efforts are being made to conserve these sites. However, a controversial recent suggestion, that some monarch populations may not migrate at all, has jeopardized some of these efforts. This article assesses the evidence for and against the new suggestion.