Do a search on ants on peonies. The ants are eatting the sticky sap that forms on the flowers. If you want to cut and bring flowers into the house cut the stems long, shake the blooms to remove most of the ants, the put blooms in water and leave outside over night. You may have one or two ants left but it is easier to brush a few. The ants do not harm the peonies and they were in the ground somewhere near the peonies anyway.

There is a questions that ants are needed to remove some of the sap from the buds before the blooms will open in full. This has been found to be incorrect. However in my observations the really older lactiflora's will open further if the ants are on the buds. The difference is very small and would not be noticed by most. The outer bud portion will split on these when many ants are present and be unsplit on those without ants.

Those of you that grow the old ones what and see what happens. You may have to put a covering on a few buds to prevent ant access.

Thanks for the response. I'm not sure why I never noticed them before.

My neighbor 'solved' her ant problem last year by cutting the peonies and hanging them upside down to dry... then bringing them in. She said they were gorgeous and held their full color, except the white. My other friend puts hers in the bathtub and rinses them. Maifleur's answer sounds simpler... I would have thought the ants would stay... worth a try.