Seeing ants on your plants, whether houseplants or garden specimens, often signals a hidden problem rather than the ants themselves being the primary concern. Ants are motivated by food and shelter, meaning their presence reliably indicates something is attracting them to the plant environment. While ants do not typically feed on plant tissue, their presence can lead to significant damage if the underlying cause is not addressed. Understanding the specific motivation behind the ant activity is the first step toward protecting the health of your plants.
The Relationship Between Ants and Sap-Sucking Pests
The most frequent reason ants inhabit plants is their symbiotic relationship with certain sap-sucking insects, a mutualism known as trophobiosis. This interaction centers on honeydew, a sugary liquid waste product excreted by pests after feeding on the plant’s phloem sap. Pests like soft scale insects, mealybugs, and aphids consume large quantities of sap to extract limited protein, resulting in the excretion of excess sugar.
Ants consume honeydew as a high-carbohydrate food source, sometimes “milking” the insects by gently stroking them with their antennae to induce a droplet of the sweet fluid. In return, the ants become diligent bodyguards, actively protecting the honeydew-producing insects from natural predators like lady beetles and parasitic wasps. By defending these pests, the ants inadvertently enable the sap-suckers to increase dramatically, leading to stunted growth, leaf distortion, and decline in the plant’s health.
The presence of ants is often the earliest sign of a pest infestation that may otherwise be difficult to spot, especially with small insects like scale or mealybugs. This ant-pest partnership ensures a steady food supply for the colony while accelerating the damage inflicted on the plant. Once established, ants may even move the sap-sucking insects to new areas of the plant for better feeding.
When Ants Are Nesting or Seeking Shelter
Ants may also be present on plants for reasons unrelated to honeydew, primarily seeking habitat, moisture, or other food sources. Potted plants, particularly those indoors, offer a protected environment where the loose, well-draining potting mix is easy for ants to tunnel through. This tunneling activity can disturb the root system and cause the soil to become overly aerated, leading to water draining too quickly and potentially desiccating the roots.
Ants are attracted to moisture; consistently damp soil, often resulting from overwatering or poor drainage, creates an ideal nesting ground. If a plant’s soil is very dry, ants may also move in, as arid conditions are suitable for nest construction. Beyond honeydew, ants are drawn to other sugary plant secretions, such as extra-floral nectaries—glands that secrete nectar outside of the flowers. Decaying organic matter, such as fallen leaves or old mulch, also provides a food source that encourages ants to linger near the plant base.
Actionable Strategies for Ant and Pest Removal
Effective ant removal requires eliminating the underlying pest infestation, as the ants will only return if their food source remains. The first step is to isolate the affected plant to prevent the spread of ants and pests to nearby greenery. For sap-sucking pests like aphids, mealybugs, and soft scale, a strong jet of water can physically dislodge many insects from the plant foliage.
Following physical removal, treat the plant with an insecticidal product that targets the pests directly. Horticultural oils, such as neem oil, or insecticidal soaps work by coating and suffocating the soft-bodied insects, and these options have a low impact on the environment. Repeat applications are necessary to eliminate newly hatched pests, as these products do not offer long-term residual protection.
To address the ant population, use targeted ant baits placed near the plant but not directly on the soil. This allows the ants to carry the slow-acting insecticide back to the colony. Avoid spraying ants with broad-spectrum insecticides, as this only kills surface foragers without eliminating the nest or the queen. Barrier methods, such as applying a fine layer of food-grade diatomaceous earth around the base of the pot, can also deter ants by creating a physical obstacle that damages their exoskeletons. If nesting is severe in a potted plant, repotting with fresh, sterile potting mix is the most direct solution, ensuring you remove as much of the old, infested soil as possible.