Monarch butterfly populations have collapsed by over 90% in recent decades. While invertebrate welfare is contested, the scale of this decline raises ethical questions about obligations to insects.
Whether monarch butterflies experience subjective suffering is scientifically uncertain, but the scale of population collapse represents an enormous loss of living individuals that have some capacity for information processing and behavioral response. Conservation of monarch populations protects the behavioral and ecological richness represented by their extraordinary migration regardless of the resolution of invertebrate sentience debates. The welfare precautionary principle suggests that the uncertainty about insect experience, combined with the massive scale of population losses, warrants moral consideration. Practical actions that restore milkweed and reduce pesticide exposure benefit monarchs and many other beneficial insects whose welfare status is similarly uncertain.