Monarch butterfly overwintering colonies in Mexico and California face habitat loss, climate disruption, and pesticide threats that have caused catastrophic population decline.
The scale of monarch population decline means that billions of individual butterflies that would have existed are now absent, representing an enormous loss of potential welfare subjects. Monarchs that encounter disrupted overwintering habitat or fail to reach overwintering sites die from cold exposure or starvation. Pesticide-exposed monarchs suffer impaired neurological function affecting navigation and coordination. The welfare significance of insect suffering remains debated, but the precautionary principle applied to billions of individuals experiencing stress, disorientation, and death during a catastrophic population decline suggests taking this welfare question seriously.