People who interact with or make decisions about invertebrate animals have an attitude toward them, although they may not have consciously worked it out. Three philosophical approaches underlie this attitude. The fi rst is the contractarian, which basically contends that animals are only automata and that we humans need not concern ourselves with their welfare except for our own good, because cruelty and neglect demean us. A second approach is the utilitarian, which focuses on gains versus losses in interactions between animals, including humans. Given the sheer numbers of invertebrates—they constitute 99% of the animals on the planet—this attitude implicitly requires concern for them and consideration in particular of whether they can feel...