An earthworm split in half becomes two worms
First of all, ew. Second of all, if an earthworm is cut in two it will not become two worms. The head end of the worm may live and regenerate its back end if it was severed behind the clitellum; but the old tail will die. However, the super fascinating planarian flatworm – a tiny freshwater worm from a different phylum than earthworms – is able to reform its entire body from slivers as teensy as 1/300th of the critter's original body size.