The criticism
"The sentience standard leaves insects out." Some say insects might feel good things, like smells and tastes, but wouldn't feel pain. So they wouldn't need consideration.
Answer 1: when in doubt, give consideration
There's some doubt among scientists about certain kinds of insects. But any responsible moral theory gives the benefit of the doubt when the doubt is reasonable. When in doubt, don't hurt.
Answer 2: even a small share is a lot
There are quintillions of insects in the world. Even if only a small percentage of them could feel, that would still be an enormous number of beings the standard tells us to consider.
Answer 3: if they feel good things, they can be harmed
If an insect can have good experiences, then it can be harmed by losing them, for example by dying. You don't need to feel pain to be harmed.
The evidence
The evidence that many insects feel keeps growing:
- flexible behavior, with decisions, learning, and memory;
- brains with structures called mushroom bodies, which have from a hundred thousand to a million neurons and combine information from the senses;
- brain connections organized in ways similar to those of bigger animals.
If this evidence is right, insects aren't just "living bodies": there's someone in there, probably able to suffer and to enjoy things.
In short
- When there's reasonable doubt, the standard says to give consideration.
- Even a small share of insects would be an enormous number.
- There's good evidence that many insects feel.