If I cut an earthworm in two will it grow into two earthworms?

Unfortunately not, if cut behind their clitellum (saddle) they may regrow a tail. However the tail which has been cut from the body will die. This is because the brain and the main part of their respiratory system is located between the head and clitellum.

Earthworms are very numerous, so a few lost when digging in the garden won't make a big difference, but at ESB we'd always encourage people to be kind to earthworms and not do it on purpose!