The number of monarch butterflies (Danaus plexippus) hibernating in central Mexico doubled this winter, a recovery that cheered conservationists but did not dispel fears for the insect’s long-term survival. Colonies of monarchs roosting on oyamel fir (Abies religiosa) trees in central Mexico’s mountains occupied about 1.8 hectares (4.5 acres) during the winter of 2024-25. This was up from 0.9 hectares the previous winter—one of the smallest hibernating populations on record. Though both areas sound small, scientists estimate the density of butterflies hibernating in the firs at roughly 21 million per hectare. The latest population count, published on March 6 by the World Wildlife Fund, offers a snapshot of the size of North America’s main population of the butterfly, whose multigenerational migration stretches from central Mexico to the Upper Midwest and Canada. A separate, far smaller monarch population lives west of the Rocky Mountains and hibernates in California. The... [Log in to read more]