That black nasy dirt they come packed in is old worm bedding, mostly composted peat the worms digested. I put plain peat moss in a gallon bag and add enough water to get it damp. Chill it in a frig ahead of time to repack your worms in. I lot of times I buy a few boxes of crawlers at walmart on the way home and put them in the new cold peat the night before fishing. No black mess !! The clean peat smells good and is easy to clean up with no stains.