Nature in balance: compacted clay soils present a challenge to trees- they are somewhat impermeable to oxygen which the trees’ roots need. Insect populations are an integral part of tree health. Ants like the ones that made this ant hill can help by aerating clay soils, which is not a bad thing at all. More crucially, the insects which hurt trees are normally balanced by other insects. A good arborist will understand the balance in the ecosystem and look for ways to adjust the balance. Good arborists won’t use broadcast insecticides because they throw insect populations out of balance, which often does more damage to the trees in the long run.