Monarch butterfly populations have collapsed by over 90 percent driven by milkweed habitat loss, with welfare implications for billions of individual insects annually.
Monarch butterfly welfare is uncertain at the level of individual experience but certain at the population level — the collapse of a migration involving billions of individuals represents an ecological welfare catastrophe whatever the capacity of individual butterflies for morally relevant experience. Caterpillars that starve for lack of milkweed, adults exhausted by migration to inadequate overwintering sites, and the complete severing of multigenerational migration routes represent welfare harms worth addressing given the low cost of milkweed restoration.