Monarch butterflies undertake one of the longest insect migrations on Earth. Population collapse driven by habitat loss raises questions about welfare at population scale for billions of individuals.
The welfare of individual insects including butterflies is a subject of scientific and ethical debate, but the scale of monarch population decline means that billions of individual organisms are affected by habitat loss and pesticide exposure each year. Larvae consuming milkweed contaminated with pesticides experience sublethal effects on development and behavior. Adults navigating a landscape with insufficient nectar sources face energetic deficits during migration. Population-scale habitat restoration through milkweed planting and reduced pesticide use addresses welfare at individual scale through improved nutrition, reduced toxic exposure, and more reliable migratory routes. The precautionary principle supports treating potential insect suffering as a reason to restore habitats even amid uncertainty.