Ants on Peony Flowers: An Example of Biological Mutualism

Published: May 29, 2018

Peonies, the "king of all flowers", are currently providing a spectacular display of blossom color in Missouri. However, with the development of flowers on peony plants, ants also arrive. While ants on the buds and flowers can be a nuisance, they do no harm (Figure 1). Once bloom is complete, ants will disappear from peony flowers and move on to find a food source elsewhere.

Figure 1 Ants searching for nectar on a peony flower.

Figure 2 Peony flower bud at marshmallow stage.

It is a myth that peonies require ants to bloom. The relationship between peonies and ants is a type of mutualism in which two organisms of different species benefit from the activity of one another. Peony flowers provide food for ants and in turn, the ants protect the blossoms from other floral-feeding insects.

Extrafloral nectaries are present outside of the peony flower buds. These plant organs secrete nectar, which is composed of sugars (sucrose, glucose, and fructose), amino acids, lipids, and other organic compounds that are a food source for ants. When a scout ant finds the nectar on the peony, she emits a pheromone or odor trail on the way back to her nest. At the nest, the scout alerts other ants of the food source. The recruited ants then follow the odor trail back to nectar on the peony flowers.

While the ants are feeding on the nectar, they protect their food source from other insects that come to feed on the flower buds. As each ant feeds on the peony nectar, the odor trail is reinforced until their food is gone. This type of insect behavior is an efficient means of utilizing a temporary food resource.

Because the presence of ants on peony floral tissues is only temporary, the application of an insecticide is unnecessary. When cutting peonies at full bloom for use indoors, hold them upside down by the stem just below the flower and shake the ants off outdoors or gently rinse the ants off before arranging them. To ensure ant removal, cut plant stems when flower buds are at the "marshmallow stage" and rinse off any ants with water before bringing them indoors (Figure 2). At this stage, flower buds are still closed but showing some color. Flower buds will also be soft when gently squeezed between the forefinger and thumb. When buds cut at marshmallow stage are brought indoors, full bloom typically occurs in 8 to 48 hours when stems are placed in water. Cut stems with flower buds can also be stored in refrigeration to produce blooms later.

Unlike ants, thrips are a common insect found feeding on peony flowers. These small (1 to 2 mm-long), slender insects pierce the flower petals with their mouthparts and extract liquids from the plant tissues, causing discolored or blemished blossoms. However, heavy infestations that destroy peony blossoms are a rare occurrence. For more information about growing peonies, see a recent IPM article: Plant Peonies in September.