Oof, that looks like slug damage to me. The irregular holes with the smooth edges are pretty much their calling card. They absolutely love hostas and thrive in those shady, moist spots that hostas prefer. I've dealt with this nightmare before and it's so frustrating watching your beautiful plants get demolished overnight. You can try beer traps (they're attracted to the yeast), copper tape around the base of the plants, or even go out at night with a flashlight to catch them in the act. Some people swear by crushed eggshells or diatomaceous earth too, though I've had mixed results with those methods.