Invertebrates represent the vast majority of animal species on Earth. Growing scientific evidence of pain sensitivity and sentience in some invertebrate groups raises important ethical questions about their welfare.
The welfare of invertebrates presents one of the most challenging frontiers in animal ethics. The sheer numbers of invertebrate animals, combined with growing evidence of their capacity for nociception and possibly subjective experience, means that how we treat them collectively has enormous moral significance. Decapod crustaceans have the strongest welfare case, supported by behavioural, neurological, and physiological evidence. Insects present a more uncertain picture: their small nervous systems, alien architecture, and different evolutionary lineage make inference from vertebrate sentience models difficult. Nonetheless, a precautionary approach that avoids unnecessary invertebrate suffering is increasingly justified by scientific evidence.