The welfare of invertebrates — insects, crustaceans, and other non-vertebrate animals — is an emerging area of welfare science with significant implications given the extraordinary numbers of these animals affected by human activities.
Invertebrate welfare presents the most fundamental challenge in welfare science: determining which animals are morally relevant without the behavioral indicators that are reliable in vertebrates. If even a small fraction of invertebrates are sentient, the welfare implications are staggering given their numbers. The precautionary principle suggests that where there is reasonable evidence of sentience-like responses — nociception, avoidance learning, behavioral flexibility — we should extend some moral consideration. The evidence for decapod crustacean sentience is now considered sufficient to warrant regulatory protection in the UK. For insects, the evidence is more contested but growing. The moral cost of treating potentially sentient creatures as though they are definitively non-sentient when the question is unresolved could be very large.