While I’d heard a fair bit about leaf miners my first run in with them came this fall on the tomatoes I planted. You can easily identify the damage. It looks like someone took a beige marker and drew a squiggly line all over several leaves. They are especially fond of vegetable crops.
Leaf miners are actually fly larva. The feed between the top and bottom of your plant leaves on the inside of the leaf. As you can imagine this makes it very difficult to do anything about them.
In all but extreme cases they do little damage to the crop and are not something to be overly concerned about.