These furious workers tend to make themselves known as the summer progresses and the soil dries. If left unchecked their hills can grow rather swiftly and make mowing a bumpy affair. The best weapon is vigilance. Once you begin to notice small hills appearing take a stiff broom and knock them down, this will keep the disruption to your mower at bay for the relatively short period of time the ants are active. If your lawn has a legacy of ant hills from summers past then they may need cutting from the lawn with a spade and the area reseeding.