We have quite a lot of ants in our garden. I've always thought of them
as benign, and just ignored them. But, earlier this year, a basil was
mysteriously cut off, right at ground level. Now, I see a collard
dying, with a great activity of small black ants right at the base of
the stem. It looks like they're attacking the plant.

Do ants do this? Is there a way to control them?

Thanks,
George