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These tiny (3 to 4mm) black ants can be seen foraging on peony flower buds.
They appear to be attracted by very tiny droplets of nectar that are exuded from the surface of these buds.
Perhaps they are also waiting for the buds to burst into flower, after which they can be found

inside the luscious, pink blossoms.
I believe the ants are Prenolepis imparis, known as "Winter Ant" and also as "False Honey Ant".