The fact that an insect is eating your plants doesn’t necessarily mean you need to get rid of it.  Spend some time observing it and reading up on it before you rush to judgment.  More often than not, you’ll find that insects are not causing significant damage.  Leafminers, for instance, often cause concern because they leave conspicuous trails, but with a few exceptions the problem is entirely aesthetic.  Learn to appreciate these trails as harmless–and often fascinating–signs of tiny animals living their lives, and you will find that suddenly they aren’t pests anymore!