From the perspective of the peony plant (Paeonia spp.), ants are not pests but temporary partners in a mutualistic relationship. The relationship begins at a specific stage of the peony's development: the bud phase. The outer layer of the peony bud secretes a sugary, nectar-like substance known as extrafloral nectar. This secretion is a deliberate physiological process by the plant, designed to attract ants. The ants are drawn to this rich food source and will diligently harvest it from the buds.
The peony's primary goal is to protect its valuable, soon-to-open buds from potential threats that could hinder its reproductive success. The most significant threats are often herbivorous insects, such as thrips or beetle larvae, that would chew on and damage the tender petals and reproductive structures inside the bud. By attracting a population of aggressive, food-motivated ants, the peony effectively hires a mobile defense force. The ants, while foraging for the nectar, will aggressively patrol the buds and drive away or prey upon these smaller, soft-bodied insects that are harmful to the plant. This form of biological pest control is highly beneficial to the peony, ensuring its flower can develop and open without being disfigured or destroyed.
A common myth suggests that ants are necessary to help the peony buds open by "licking the sticky nectar off." From the plant's physiological standpoint, this is incorrect. The opening of the bud is an internal process driven by plant hormones and turgor pressure within the cells. The ants play no role in mechanically forcing the buds apart. The secretion of nectar is purely an attractant to bring protective ants to the site; the bud is programmed to open regardless of whether an ant has visited it. The presence of ants is a strategic advantage for protection, not a requirement for the blooming mechanism itself.
While the overall interaction is positive, a very large population of ants can sometimes create a secondary issue. If the ant colony is exceedingly numerous, their farming practices might become a minor concern. Some ant species "farm" aphids for their honeydew excretion. An ant population attracted to the peony's nectar might subsequently move aphids onto the peony's stems or the undersides of its leaves to establish a new food source. The aphids themselves can then weaken the plant by sucking its sap. However, this is a secondary and indirect effect, not a direct result of the ants feeding on the bud's nectar. The peony's own strategy has, in this scenario, inadvertently attracted a new pest.
