Generally, we tell students that if you cut a worm in half, you will most likely end up with two dead pieces of worms. However, if you are lucky, the piece with the head may grow a new tail, so you will have one alive worm and one piece of dead worm. Some worms have a natural reflex, in which they will eject their tail when the tail is pulled. For example, when a bird catches the tail end of a worm, the worm would eject or sever its' tail from the rest of its' body. Thus, the worm remains alive and safe, while the bird gets only part of the worm.
Worm compost makes nutrients available to plants.