The question of whether invertebrates experience pain in a morally relevant sense is one of the most active frontiers in animal sentience science, with significant ethical and welfare implications.
Invertebrate pain research is advancing our understanding of the distribution of nociception and potentially conscious pain experience across animal taxa. The evidence is strongest for decapods and insects among invertebrates, with more uncertain evidence extending to smaller invertebrates. The ethical implications depend on both whether invertebrates experience pain and how to weigh uncertain probability of experience against the scale of invertebrate populations. A precautionary approach that reduces unnecessary harm to potentially sentient invertebrates is defensible even under uncertainty.