Peonies have glands called extra-floral nectarines that deposit sap on the buds. This sap is made up mostly of sugar but also contains protein, amino acids and other nutrients.
Even though ants are not instrumental in opening the buds, they do serve a purpose. Ants are aggressive and will either eat or drive other pests away that harm peonies. Therefore, it is best to just leave them alone and let them feast on the sap.
Ants do not stay around long after the flowers bloom and the nutrient-rich sap is no longer produced. It is only created while the flower is still a bud. A few ants may be reluctant to leave the flowers, but once they are fully open, the ants will be gone.
It is important to prevent bringing ants inside when using peonies as cut flowers. Cut the flowers and dip the head of the flower in a bucket of clear water. Gently swish it around until all ants fall into the water. Remove the flower from the water and shake gently to remove excess water .