Peppermint essential oil – you can get it lots of places including Whole Foods. Put a couple drops at the end point of where they have arrived and they will reverse course on their own. I don’t like to kill them so that’s what I do. You can also use your finger to smear a line of it and they won’t cross it. The first ones might as the smell confuses them and they run around a bit. Wash your hands after and don’t touch your eyes! It is very strong, but non toxic. I have reversed a 100′ foot line that way – took a couple hours but they did not come back. And that line was like 1″ thick! Then note where they came in and caulk that hole.