When they become a problem:
If your seedlings are being eaten and you see half a dozen or more earwigs scatter when you lift a leaf it's time to act. The organic gardening books suggest trapping by rolling placing a rolled up dampened newspaper next to the plant. The earwigs will crawl inside and hide during the day. That's when you dump them into a container of soapy water. A more effective method might be the use Organic Preen with Spinosad.