Did you know that ants on your peony buds is perfectly normal if not beneficial to the opening of the flower bud. It is believed that the small amount of nectar on the bud attracts the ants which help to open those dense flower buds.  An old wives tale, maybe, but there certainly is no harm to them being there.  No need for treatment, let the ants stay a short while. Once those bloom are open they will be gone.
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Enjoy those beautiful fragrant blooms!