Invertebrate welfare consideration is expanding beyond insects to include earthworms, molluscs and other species as understanding of their neural complexity grows.
The expanding circle of moral concern is pushing into genuinely uncertain territory with invertebrates beyond the decapod crustaceans now covered by UK sentience legislation. Earthworms, snails, slugs and various marine invertebrates show behavioral responses to noxious stimuli that, in vertebrates, would be considered pain indicators. The neural simplicity of these animals relative to vertebrates creates genuine scientific uncertainty. However, the precautionary argument — that if there is meaningful probability of suffering, we should take steps to minimize unnecessary harm — applies here as well. Agricultural practices that cause mass invertebrate deaths, and pest control methods that cause prolonged invertebrate suffering, deserve more consideration than they currently receive.