The monarch butterfly migration is one of nature's most extraordinary phenomena, but the welfare of billions of individual monarchs during migration is affected by milkweed loss, climate disruption, and habitat fragmentation.
Whether insects experience suffering in morally significant ways remains scientifically uncertain. However, the scale of monarch population collapse means that even small individual welfare probabilities represent large aggregate welfare impacts. Butterflies exposed to sublethal pesticide doses show impaired navigation - potentially condemning them to failed migration and death. Caterpillars starving on milkweed-depleted landscapes face death from nutritional failure before completing development. If monarchs have any capacity for distress - as their complex neurological system may allow - then the billions that fail to complete their migration annually due to human-caused habitat destruction may experience something analogous to suffering at an enormous scale.