Pesticides and herbicides kill good bugs as well as the bad bugs. That is one of many reasons why industrial agriculture is unsustainable. John Michael Greer describes the role of the earthworm in this excerpt from Animals I: Birds, Bats, and Bumblebees.
A garden is an ecosystem managed in such a way that human beings get to eat a significant fraction of the net primary production of the plants that grow there. Net primary production? That’s the amount of energy each year that the plants in a given ecosystem take in from the Sun and store in the form of sugars and other compounds that can be eaten by some other living thing. Everything other than plants in any ecosystem gets its fuel from the net primary production of that ecosystem, or of another ecosystem that feeds energy into it.
You’re not going to get anything close to a majority of the net primary production of your garden onto your dinner table, by the way, and it’s a mistake to try; if you do, you’ll starve other living things that depend on a share of net primary production to keep their own dinner tables stocked, and you need these other living things in order to have a healthy and productive garden. (Ignoring this latter point is one of the critical errors of today’s industrial agriculture.) Your goal instead is to make sure that as much of the net primary production diverted from your table as possible goes to living things that earn their keep by doing something for your benefit.
Here’s an example. A certain amount of each year’s net primary production from your garden goes to feed earthworms. Any gardener with the brains the gods gave geese won’t grudge them their share, because earthworms break down organic matter into forms plants can use, and they improve the texture and drainage of soil as they do it. Charles Darwin – yes, that Charles Darwin – wrote a brilliant and too often neglected book on the role of earthworms in the creation of topsoil; what he found, to drastically simplify a classic piece of ecological research, is that earthworms are topsoil-making machines, and the more you’ve got, the better your soil and the higher your crop yields will tend to be.