Monarch butterfly populations have crashed by over 80% in recent decades due to habitat loss, pesticides, and climate change — raising questions about insect welfare at population scale.
Whether individual monarch butterflies have morally relevant welfare experiences remains scientifically uncertain — insect sentience is an active research frontier. However, the massive scale of monarch decline (hundreds of millions of individuals lost) means that even a small probability of individual experience creates significant expected welfare relevance. At the population level, conditions that cause mass mortality events — pesticide exposure, extreme weather, habitat destruction — likely involve acute distress even if the nature of that distress differs from vertebrate pain. Monarch conservation is justified on multiple grounds: ecological function, cultural significance, and precautionary welfare concern for insects. The uncertainty about insect sentience is not a reason to dismiss welfare concerns — it is a reason to weight them appropriately given the scale.