Snail, slugs, flea beetles, and some caterpillars could be doing this, Plantdiva. Flea beetles operate during the day, and are pretty obvious--they are iridescent dark blue, green, or black round beetles about the size of a standard pinhead. Distinctively, they also jump like fleas when disturbed. Otherwise, I would go out at night with a flashlight to see who the culprits might be, since most others are active after dark. Snails and slugs can be controlled with iron phosphate granules, such as Sluggo, and the caterpillars can be controlled with Bacillus thuringiensis (Dipel dust) or spinosad. The latter will also control flea beetles.