Flat Worms

Me again!

I was digging over a patch this weekend (yep we had enough dry weather on Sat to just about fit it in) And I kept on finding some slug/worms which I've since found out are flat worms.

I'm been told they eat the earthworms (?) which for me doesn't seem so good. Grandad alway's swore by earthworms.

Is there anyway I can reduce thair numbers without harming the earthworms (I realise I'll never completely get rid of them)

Thanks in advance for sharing your knowledge, it's really appreciated!