Anyone who has a colicky baby knows full well they can feel pain.
Anyone who who has baited a hook knows that an earthworm very likely feels pain.
Call it what you will, but unpleasant physical stimuli cause a response.
Worms can't scream as they are impaled on a hook, either.
Nerve development is happening by the first three weeks (first trimester).
These people can lie all they want to feel better about what they are doing, but that won't change reality.