I have a small garden in my backyard (a 4x4 "square foot" garden). It has a variety of different plants in it. Recently I tried to grow melons in it (watermelons and cantaloupes). But, shortly after it grows a couple leaves I return the next day to find the leaves torn off the stem of the plant. Just the stem is left and torn pieces of the leaves. My other plants don't have this problem, it's just the melons. I replanted, and the same thing happened again. What could be doing this and how can I defend against it?
The photos below are from other plants in my garden that were damaged in similar ways. I'm not sure if it is from the same pest or not, but maybe it will provide a clue.