Like all living animals, worms need oxygen. However, they can’t breathe with their mouths… and since they don’t have a nose, well that’s out, too. 

Oh, BTW, they don’t have a set of lungs either!

So, just how do they breathe? Fascinatingly, worms have thin permeable skin through which oxygen can pass. The mucus on their skin helps this process. Therefore, the moisture level of a worm’s environment needs to be just right. If it dries out, they suffocate.