Peonies are large-headed flowers that grow on shrublike plants. Ants have long been thought to be responsible for helping the peony open its buds. Certainly ants can be found on many peonies in the spring, but the reason has nothing to do with helping the flower open.
Peony blossoms have tiny glands along the scales that cover the closed buds. These glands produce sweet nectar.
Ants are drawn to the sweet nectar, a mixture of water, sugar and amino acids. As they swarm over the buds, it appears as if they are in a feeding frenzy and may actually be contributing to the bloom of the bud. However, they are simply collecting food.
The ants do not have any effect on the opening of the peony bud. It would open in the same time frame whether the ants were present or not. The ants do provide protection for the peony against other pests that might feed on the bud, but they are simply protecting their food supply.