whatever it is its a chewing insect, like a catapilar or grasshopper, these are easier to control than sapping insects like thrips. you could grow some garlic or mint along side the cannabis to discourage them. another way is to make a spray from fresh jalapeno and garlic. just blend them in a blender, add about 90% water to the mix, then filter it with pantyhose, add a drop or two of dish soap (or other wetting agent) and put in a sprayer. spray all leaves, undersides too, this is a safe way stop chewing insects.