United Kingdom 
Last year the buds on my Sarah Bernhardt peony did not open properly. This year I have noticed ants crawling all over the buds. Are they doing the damage or are they predators on something like aphids who are doing the damage.
28 May, 2010
Many ants actually farm aphids (and a few other sucking insects) like cows, keeping them in their nests through the winter, placing them carefully in spring, "milking" them of honey dew, and protecting them from predators. Heavy aphid infestations can distort new growth and flower buds, so they may be the problem, and ant control is probably part of the solution. I would scatter ground up orange peel aroud the base of the plants, to repel the ants, and spray the new growth with a weak dish soap solution, maybe 5 ml per liter of water. Good luck!
28 May, 2010