Earthworms are critical soil engineers whose populations have declined dramatically from tillage, pesticides, and soil compaction, with welfare implications that are scientifically contested.
The sentience of earthworms is genuinely scientifically uncertain, but their role as prey for definitively sentient species and as ecosystem engineers is beyond doubt. Earthworm mass mortality from pesticide application eliminates the food supply for millions of surface-feeding birds, causing nutritional stress and reduced breeding success. Agricultural soil management that destroys earthworm populations has cascading welfare consequences for all species dependent on healthy soil ecosystems, from birds to badgers to hedgehogs.