Herb Paris

This unusual plant consists only of one whorl of four leaves with a green flower on top.
I planted out a (rather expensive) pot full early in the spring, and watched them gradually emerge. Then one day I discovered that some creature - slug, mouse, deer, dog? - had snapped off three heads and left them lying on the ground.
Rather irritating!
However, the remainder seem to be ok. I was wondering how they increase? Or perhaps they will just disappear over the winter. We'll see!