Monarch butterfly populations have declined by 90% in eastern North America since the 1990s. While traditional welfare frameworks focus on vertebrates, the scale of monarch decline raises important questions about insect welfare.
Monarch welfare sits at the frontier of animal sentience science. Insects possess nervous systems far simpler than vertebrates, and the evidence for insect sentience — though growing — remains more uncertain than for fish or crustaceans. However, the scale of monarch population collapse raises welfare considerations even under uncertainty: the loss of hundreds of millions of individuals annually, each dying from habitat loss, pesticide exposure, or climate disruption, constitutes potential welfare harm at enormous scale. Beyond individual welfare considerations, monarchs represent an ecological welfare bellwether — their decline reflects the degradation of agricultural landscapes that also affects countless other insect species whose contributions to ecosystem function and welfare are profound.