Monarch butterfly populations have declined 80-90% over recent decades. Their welfare and conservation illustrates the challenges of protecting small animals at massive scale.
Monarch welfare sits at the uncertain frontier of insect sentience — whether individual monarchs experience their migration, starvation, or parasitism in a morally relevant way remains genuinely uncertain. However, the scale of population decline — hundreds of millions of individual animals whose lives are cut short by habitat loss and pesticide exposure — is significant regardless of individual sentience. The loss of milkweed from agricultural landscapes means larvae that hatch find no food and die. Caterpillars parasitised by fly larvae experience a physiological process that may involve suffering. The precautionary principle suggests taking monarch welfare seriously while acknowledging uncertainty, and the conservation case for protecting monarchs is strong independent of welfare considerations.