I have a big problem of ants in my garden, black ones which seem to love nesting in the base of some of my big plant pots and they can disturb the roots enough to damage plants, or even kill them. I guess your peony isn't in a pot? Then you need to put some ant killer onto the ant nest. I had it last year next to my rose bush. I also put a ring of ant powder around my rose a few times until all was clear. I have a problem with black ants, thousands of them in our garden and they love my pots. I have to keep the pots on a little pile of ant powder all summer long, it's enough to put them off using them. They are welcome in my garden, to an extent!