They are sensitive to light, and try to hide when exposed to light. It is in the first segment. There is a small protruding lip just over the mouth. When foraging, this lip will be stretching out for sensing his food. No, they grind food in their gizzard by muscle action.
Earthworms have a muscular gizzard.
Small parts of food, mixed with some grinding material such as sand, topsoil, or limestone is ingested. Contractions from muscles in the gizzard compress particles against each other, mix it with fluid, and grind it to smaller pieces. A constant supply of fresh air is needed by the earthworms. Earthworm compost can be used like any other compost, for mulch, fertilizer, soil conditioner or amendment. Sterilizing is not necessary.