Woodlice

Woodlice are usually found where there's dead or dying damp leaves and debris. I find them under pots if I move them. I don't find that they cause any problems with the living plants, though. Could it be some other beastie that's to blame?

Woodlice don't eat living plant material and therefore are not to blame for any damage to your plants. As Spritz says, they eat dead material - mostly rotton wood. Maybe your compost has a high wood content?