Ants like peonies. When I was about three, my mom told me that ants would help the peonies bloom. whenever I saw an ant in our yard, I'd pick it up and dutifully deposit it near our peony plant. That peony never did very well, and the ants never stuck around (or maybe they just didn't survive being pinched between my clumsy toddler fingers). An internet search reveals that it is probably a myth that ants promote peony blossoms. The ants like the sweet nectar exuded by the flower buds... They may or may not benefit the plant by eating smaller insect predators or enriching the nearby soil with their colonies.

This photo was taken on my last evening in Saskatoon, where the peonies were always swarming with ants. I left Saskatoon before our peonies bloomed, and arrived in Ottawa right after theirs had finished.