I needed to get rid of a new ant hill immediately, because I couldn't move the temp run and the chicks didn't know to stay out of the ants. Poor babies were walking in and then picking up their feet and looking at them and pecking them. I'm sure they were getting bitten.
I boiled some water and poured it on the ant hill. You have to be VERY CAREFUL to keep chickens away, especially if they think anything you bring is a treat. I stayed there and kept them away from the place until it cooled, which took some time. It doesn't kill all of them, but probably about 95% in my case, which at least let the chicks use their run for the next few days, which was my main goal.
I don't know if your situation is similar. If I had had time to kill them, I would not have chosen this method, I think.
trish