Invertebrates make up over 95% of all animal species, and evidence for sentience in at least some invertebrate groups is growing — raising questions about the scope of our moral obligations.
The question of invertebrate welfare sits at the scientific and philosophical frontier. For some groups — particularly decapod crustaceans like lobsters and crabs, and cephalopods like octopuses — the evidence for sentience is strong enough that precautionary welfare consideration is warranted and increasingly legally required. For insects and other arthropods, the evidence is more uncertain but growing. The precautionary principle suggests we should err on the side of reducing potential harm even under uncertainty, particularly given the enormous numbers involved. This is an area where welfare science and ethics are rapidly evolving.