Monarch butterflies undertake one of nature's most remarkable migrations to overwinter in Mexican mountain forests now threatened by logging and climate change.
Monarchs are social insects whose overwintering strategy depends on clustering for thermal regulation. Habitat loss forces smaller, less thermally stable clusters that expose millions of butterflies to fatal temperature extremes. While individual insect sentience is less established than for vertebrates, the precautionary principle and the scale of decline warrant concern. The disruption of a migration that took millions of years to evolve represents an ecological and potentially welfare-relevant loss at massive scale.