Monarch butterfly populations have declined by more than 80% over three decades, with habitat loss and insecticide use threatening both individual welfare and the ecological services these insects provide.
Monarch butterfly sentience and capacity for welfare is uncertain but their behavioral complexity - multi-generational migration navigation, mate selection, and host plant assessment - suggests some degree of experience. The welfare dimension of population decline extends to the ecological services monarchs provide and the human welfare value of their presence as cultural and ecological touchstones. Individual monarchs experiencing pesticide exposure show behavioral impairment that likely involves some form of distress. Taking the precautionary approach to potential insect welfare while protecting their ecological role is the appropriate response.