Monarch butterfly populations have declined by over 80%, with welfare considerations entering conservation discussions as evidence of insect sentience grows and conservation organisations recognise individual welfare.
Monarch butterfly welfare sits at the frontier of expanding welfare consideration. While monarchs have simple nervous systems compared to vertebrates, evidence of associative learning, navigation ability, and stress responses to adverse conditions suggests some capacity for welfare-relevant states. The mass mortality events during severe winter storms at overwintering sites, the physiological stress of the extraordinary migratory journey, and exposure to insecticides throughout the breeding range represent potential welfare harms that become morally relevant if the moral case for insect welfare is accepted. Conservation of milkweed habitat and reduction of insecticide exposure would improve both population outcomes and individual welfare under a precautionary framework.