Monarch butterfly populations have collapsed by over 80% in recent decades, with mass migration failure representing a welfare and conservation crisis.
While the capacity for suffering in insects is uncertain, monarch butterflies face population-level collapse that eliminates the ecological conditions for their evolved behaviours. Caterpillars exposed to pesticide-contaminated milkweed experience developmental disruption and death. Adult mortality during migration through increasingly fragmented landscapes represents a welfare consideration at population scale under precautionary frameworks.