The monarch butterfly migration is one of the most remarkable animal journeys on Earth, and the welfare of individual butterflies during this multi-generational migration is shaped by climate and habitat quality.
Monarch butterfly welfare during migration involves the energetic challenge of navigating thousands of kilometers while finding adequate nectar sources for fueling flight and milkweed for reproduction. Climate change is creating mismatches between butterfly phenology and plant availability along the route. Individuals that cannot find adequate fueling stops during migration arrive at overwintering sites in poor condition or fail to arrive at all. While insect sentience remains uncertain, the scale of monarch decline — from hundreds of millions to thousands — represents a potential welfare loss of enormous magnitude if monarchs have any capacity for experience, alongside the ecological significance of their loss.