Does anyone have any tips on finding worms besides digging for them?

We have a worm bed that we are trying to build up to have plenty of bait to fish this spring and summer. We've tried digging holes, leaving wet cardboard overnight and other things and haven't had much luck at all. Our weather here has been kind of spastic..in the high 60s last week and low 40s this week so i don't know if that has any bearing on finding worms or not. Any tips, tricks or suggestions are greatly appreciated! Thanks!