The sight of ants crawling on a hydrangea often leads gardeners to assume the plant is producing a sweet substance that attracts them. However, the hydrangea itself is rarely the primary target. The true reason for the insect activity involves a complex food chain unfolding on the leaves. This subtle biological interaction transforms the flowering shrub into a temporary feeding ground for ants.
The Direct Answer: Hydrangeas Are Not Ant Food
Hydrangeas do not typically produce the high-sugar nectar or sticky exudate that ants rely on for sustenance. Ants are driven by a need for carbohydrates, and the plant’s natural chemistry usually does not meet this requirement. For example, popular mophead varieties feature large, showy flower clusters composed mostly of sterile florets that contain little to no nectar.
While some native varieties, like Oakleaf hydrangea (Hydrangea quercifolia), offer accessible pollen and nectar that attracts true pollinators, the large number of ants observed is not due to the flower’s output. The presence of ants signals that a different, more enticing food source is being produced elsewhere on the foliage.
The True Attractant: Hidden Pests and Sugary Secretions
The actual substance drawing the ants is honeydew, a sugary waste product. This sticky, clear liquid is excreted by small, sap-sucking insects that feed on the hydrangea’s internal fluids. These pests pierce the plant’s vascular tissue (phloem) to extract nutrient-rich sap.
Since the sap contains high sugar levels relative to the proteins the insects need, they must ingest large amounts of fluid. They excrete the excess sugar and water as honeydew. Common culprits include aphids, scale insects, and mealybugs. These pests often hide on the undersides of leaves and new stems, making them difficult to spot. The sticky honeydew coats the leaves below the infestation, providing a highly attractive carbohydrate source for ants. A visible sheen on the leaves is often the first sign of a hidden pest problem.
Understanding the Ant-Pest Symbiosis
The relationship between ants and honeydew-producing insects is an example of mutualism, often called a feeding partnership. Honeydew is a desirable food source, and ants essentially “farm” the pests to ensure a continuous supply. Ants patrol the stems and leaves, collecting the honeydew directly from the insects’ bodies.
In exchange for this sugary payment, the ants provide protection. They aggressively defend their food source by attacking natural predators, such as lady beetles and parasitic wasps, that would otherwise control the pest population. Some ant species even use their antennae to stimulate aphids to produce more honeydew. This defensive behavior allows pest colonies to thrive and multiply without predation. Therefore, a significant ant trail on a hydrangea is strong evidence of a severe, pre-existing infestation of sap-sucking pests.
Identifying and Addressing the Root Cause
Since ants are a secondary symptom, effective management requires eliminating the primary pest population. Inspection should concentrate on new growth, buds, and the undersides of leaves where honeydew producers congregate. Honeydew also creates a secondary problem by hosting sooty mold, a black fungus that blocks sunlight and reduces photosynthesis.
Small infestations can often be managed by dislodging the pests with a strong spray of water. For persistent issues, horticultural oil or insecticidal soap offers a targeted treatment. These products smother the soft-bodied insects without harming the plant. Thorough coverage of all infested areas is required to break the honeydew cycle. Once the sap-sucking insects are controlled, honeydew production ceases, and the ants will move on.