Monarch butterfly populations have declined by over 80% in recent decades due to milkweed loss, climate change, and pesticide use, with habitat restoration and reduced pesticide use offering meaningful recovery pathways.
Whether insects experience welfare harms in a morally significant sense remains scientifically contested, but the precautionary principle and the sheer scale of monarch mortality — billions of individuals annually — make their population decline worthy of consideration. Monarch larvae that encounter pesticide-contaminated milkweed experience reduced survival and developmental abnormalities. The collapse of migration routes and overwintering habitat leaves monarchs vulnerable to starvation, exposure, and predation at critical life stages. Regardless of uncertainty about insect sentience, the ecological significance of monarch population collapse — for plant pollination, for the broader insect biomass that sustains bird and bat populations — makes monarch conservation a high-priority wildlife welfare concern.