From the perspective of the peony plant (Paeonia spp.), the presence of ants is not a sign of distress but rather a component of a mutually beneficial, or commensal, relationship. The primary interaction begins with the peony's flower buds. As these buds develop, they secrete a sweet, sugary substance known as extrafloral nectar. This nectar is not produced to attract pollinators for the flower itself but is a strategic offering to attract ants. The plant provides a valuable food source, and in return, it gains a formidable army of protectors. The ants, while harvesting this nectar, aggressively defend this rich food source from other insects that may pose a genuine threat to the plant, such as herbivorous beetles, caterpillars, or other bud-eating insects. For the peony, this is a highly effective form of organic pest control.
A common myth suggests that peony buds require ants to chew on the buds to help them open. From the plant's physiological standpoint, this is entirely false. The process of bud opening (anthesis) is governed by internal hormonal signals and environmental factors like temperature and light. The sticky bud coating that attracts ants is simply a biological attractant and has no mechanical function in keeping the bud sealed. The ants' activity does not force the buds open; the plant opens them on its own schedule. The relationship is ecological, not mechanical. The peony does not rely on the ants for this fundamental physiological process.
While generally harmless or even beneficial, the interaction can occasionally tip towards being slightly detrimental from the plant's viewpoint. The immense attraction of the extrafloral nectar can draw very large numbers of ants. In their fervent harvesting, some species might occasionally nibble on the very outer petals or sepals of the bud, causing minor cosmetic damage. Furthermore, if an ant colony discovers a wound or a crack elsewhere on the peony's stem, they might exploit it to feed on the plant's sap, which is a valuable resource the plant must then expend energy to replace. However, this is not a common occurrence and is typically insignificant compared to the damage prevented by their protective services.
Weighing the costs and benefits, the peony's evolutionary strategy of producing extrafloral nectar is a net positive. The energy expended in creating the sugary substance is a worthwhile investment for the significant protection gained against more damaging pests that could destroy buds entirely, hamper photosynthesis by damaging leaves, or otherwise reduce the plant's vitality and reproductive success. The minor and occasional nibbling or sap-feeding is a small price to pay for this security detail. Therefore, the presence of ants is interpreted by the plant not as an infestation, but as the successful activation of a built-in defense system. The relationship is a fascinating example of co-evolution where the plant cleverly uses a food reward to manipulate the behavior of ants for its own benefit.
