My runners are super duper foragers!
I did not do a scientific study, but I estimate that the slug population dropped 80 to 90 percent in the time I have had the runners, which is almost three years now. They eat slugs, squash beetles, japanese beetles, slug eggs, grubs and worms.
And they...
I believe Sweet Folly has hook bills (they are on my list of someday maybes) and I believe they are similar to runners in their (in)ability to fly. So I don't think they would be any more of a concern than most mallard-derived domestics that way.
I found out about them after I started with...