Leaf miners

Upon closer inspection today, it looks like little white caterpillars are consuming the leaves of my chard and spinach. It still looks like a disease because you never see the worms until they're so big and the leaf is so disintegrated that they're visible through the remnant membrane, so that's why I thought it was mildew before.

I spent about half an hour picking off all my attacked spinach and chard leaves. I probably should have done that when I first noticed the condition. Hopefully it will make a positive difference.

Update: Jon informs me that these are, in fact, leaf miner larvae. I'm investigating it.

Update #2: Okay, these are definitely leaf miners, because this page describes my dilemma very accurately. They suggest picking off the infected leaves as the first method of control (just as I have been doing). Beyond that, there's not much you can do, unless you want to take the pesticide route. I can see how farmers would be tempted by that option if they have a large crop at risk. The sad thing is, by applying pesticides you damage soil life, which is crucial for healthy soil. And as Jon and I have learned, healthy soil = healthy plants.