Something is Eating My Swiss Chard

It could also be slugs or snails that munch at night, check to see if there is any slime trails. If so, it is those little beasts!

Soft-bodied insects (mites, aphids, mealybugs): Mix one tablespoon canola oil and a few drops of Ivory soap into a quart of water. Shake well and pour into a spray bottle. Spray plant from above down, and from below up to get the underside of the leaves. The oil smothers the insects.
Good luck.