The only suggestion I have which is not very useful in pot situations. They love carrots and if you bury a carrot ( has to be homegrown or organic as the shop ones have chemicals to deter hem) near the affected plants they go inside this, you can then pull out the carrot and dispose of the blighters. I sometimes have a problem when I have broken in a new piece of ground, as David says they are prevelent in pasture, when I planted out a new bed of Primula vailii they attacked them. I caught quite a few with the carrot method, I don't know if it affected the numbers in the primula bed but at least you felt satisfied catching them. I don't know how they arrived in the pots.