How do I get rid of Green worms in basil?

I am struggling with the same problem. So far I am resorting to carefully inspecting my plants (indoors in pots since it is November in Ohio) each day, but have found the worms very difficult to see, even when large. This morning I gave the plant a vigorous shake and 2 worms fell out, so I plan on shaking every day. Does anyone know if the worms are hatching from the soil? Next I plan on scraping out the top layer of soil and replacing.