Jerks in the Garden

Just when you begin to fancy your thumb greener than you expected...You might even start feeling a little proud of your efforts to protect and nourish those once cute and tender lettuce starts. Perhaps you're seeing the fruits of your success in nurturing them into prolific, lush, salad-producing plants a la this:

Fancy that. Nice work, you! But then you notice things have started to look a little less than savory:

Grrrrr....Seriously, what is that? Upon closer investigation, you find the culprit(s):

Oh nature...you saucy minx. Just when I think I've figured you out, you throw this curveball in the shape of these hungry crawlers. Can't say the kids book didn't warn us. Thank you farmers who actually do this for a living and not a hobby. To that end, what do you do about these jerks?