Probably slugs, they love hostas. Did you notice slimy trails?

There are several ways to kill slugs and snails without using dangerous chemicals, including some slug baits that aren't toxic to pets and other critters (ex: Sluggo, which I've used with great success. Needs to be reapplied periodly -- every month or so.). See link below, or do a search, for other methods of getting rid of them. It becomes a hobby of sort for some... :)

Metaldehyde and methiocarb, found in the chemical slug baits, are dangerous if ingested by wildlife, pets, children so you might want to stay away from them.

Good luck!

Here is a link that might be useful: Go away, slugs!