The presence of ants in a garden is often viewed simply as good or bad, but their role is complex. Ants function as both industrious soil engineers and protectors of certain destructive garden pests. Their overall impact depends on the specific species and their activities. Understanding this relationship is necessary for maintaining a healthy balance, as ants can provide significant ecological benefits while also undermining plant health.
How Ants Improve Soil Health and Control Pests
Ants contribute significantly to the physical structure and fertility of garden soil through their daily activities. As they excavate their underground nests, their tunneling action aerates the soil, similar to the work of earthworms. This creation of channels improves both water infiltration and oxygen circulation, which are beneficial for plant root respiration and growth.
Ants also act as efficient scavengers and decomposers. They collect and transport organic matter, such as dead insects and decaying plant materials, back to their colonies. This process accelerates the breakdown of materials, recycling nutrients and enriching the soil with organic compounds. The accumulation of these materials within the nest increases nutrient levels, making them more available to surrounding plant roots.
Many ant species function as generalist predators, contributing to natural pest control. They actively hunt and consume the eggs, larvae, and bodies of small, soft-bodied insects, including caterpillars. This predation helps to regulate the populations of numerous common garden pests that do not produce a sugary secretion. Ants can therefore help prevent localized outbreaks of certain damaging insects.
The Detrimental Impact of Ants on Plants and Crops
The most significant negative impact of ants in a garden stems from a mutualistic relationship they form with certain sap-sucking insects. Ants actively protect, tend, and even move populations of pests like aphids, mealybugs, and soft scale insects. These pests excrete a sugar-rich liquid called honeydew after feeding on plant sap, which serves as a food source for the ants. To ensure a continuous supply, worker ants guard these sap-suckers from natural predators. By interfering with biological control mechanisms, ants increase the populations of these pests, leading to heavy infestations that stunt plant growth, cause leaf damage, and potentially transmit plant pathogens.
Ants also cause direct physical damage to plants through their nesting habits and foraging behavior. Large ant mounds built near the base of plants can disturb root systems, leading to reduced nutrient uptake and instability. Ants sometimes excavate soil from under newly planted seedlings, causing them to wilt or dry out. Certain species may also feed directly on the soft tissues of plants, such as tender flower buds or ripening fruits.
Knowing When to Take Action
Deciding whether to intervene against an ant colony requires observing their activity to determine if they are detrimental. If ant activity is limited to general foraging on the ground or in the compost heap, they are likely providing ecosystem services and should be left alone. In such cases, the benefits of aeration and decomposition outweigh any potential harm.
Intervention becomes necessary when you observe ants actively tending large, localized colonies of sap-sucking pests on your plants. The presence of ants consistently traveling up and down a plant stem, especially in combination with a visible infestation of aphids or scale, indicates a problem that requires attention. Another trigger for action is when ant mounds are built directly against the stems or roots of established plants, or if the soil is being excavated in sensitive areas like seedbeds or potted containers.