Chalk Dust and Ants

When we go camping I keep seeing these chalk lines around the area where the leveling jack stands touch the ground and now I know why! Ants wont cross a chalk line!!! I bought some of this Marking Chalk at Lowe's (by the measuring tapes and there's lots of colors) and I poured it around this active ant hole and they would not cross the line. Well, one did, he went across the narrowest part and almost turned back. I saw them try to climb across the grass to get in but only one made it out. I have always used ant poison around the jacks but then I saw a bird eating it (poisoned cornmeal) and so I would like to stick to a more environmental friendly product. Whatever you do put something around your jacks because we had some friends who had ants in their trailer after one evening at the park.