Slugs

Carrying on from how to get rid of slugs. I saw a bit on BBC news this morning concerning this problem and the lady mentioned a bug/worm that you water onto the garden and this creature burrows into slugs and kills them whilst it is absolutely harmless to everything else and, apparently, now is the time to use it.

I think it began with an 'R'. Does anyone know the name and where/how to get it.