Monarch butterfly populations have declined by over 80 percent in recent decades due to habitat loss, pesticide use, and climate change. Their welfare as potentially sentient insects and their ecological importance make conservation urgent.
The welfare status of butterflies remains scientifically uncertain — their nervous systems are far simpler than vertebrates and cephalopods, and the evidence for insect sentience is genuinely contested. However, the precautionary principle and the sheer scale of insect decline suggest that taking insect welfare seriously is warranted. The ecological welfare implications of monarch collapse extend beyond the butterflies themselves: monarchs are important pollinators and a keystone indicator species for the health of North American grassland and meadow ecosystems. The habitat loss driving monarch decline — conversion of milkweed-containing habitat to herbicide-resistant crop monocultures — also drives declines in hundreds of other insect species, many of which may have higher welfare relevance.