The Red Imported Fire Ant (Solenopsis invicta) is an aggressive, mound-building pest widespread across the Southern United States and other regions globally. These ants are known for their painful stings and the large, dome-shaped soil mounds they construct in lawns, gardens, and agricultural fields. When fire ants establish colonies near trees, homeowners often become concerned about potential damage to their landscape investments. Understanding the danger fire ants pose requires looking closely at a tree’s life stage and overall health.
The Direct Answer: Fire Ants and Tree Mortality
Fire ants can kill a tree, but this outcome is highly dependent on the tree’s age and condition. Mature, healthy trees with thick bark and established root systems are rarely killed outright by fire ant activity. These established trees can generally withstand the tunneling and foraging that occurs near the base without significant structural damage. In some cases, the ants may even provide a minor benefit by preying on other insect pests near the trunk.
The greatest danger is to young seedlings, recently transplanted trees, and trees already weakened by factors like drought, disease, or prior mechanical injury. Newly planted trees lack the robust defense mechanisms of their mature counterparts, making them highly vulnerable to attack. For these susceptible plants, a fire ant colony establishing a mound at the base can lead to rapid decline and death. This direct threat means immediate action is necessary when a mound appears near a vulnerable sapling.
Mechanisms of Injury
The primary way fire ants injure and kill young trees is through a process called girdling. Girdling occurs when the ants chew into the tree’s bark, often at the root flare or base of the trunk, to expose and feed on the cambium layer. The cambium is the thin, living tissue directly beneath the bark responsible for transporting water and nutrients between the roots and the leaves. When this layer is damaged around the entire circumference of the trunk, the flow of resources is interrupted. This interruption effectively starves the tree’s upper structure and leads to death.
Fire ant mound construction itself causes significant stress to a tree’s root system. As the ants churn the soil to build their nest, they physically disturb and expose delicate feeder roots, causing them to dry out and die. This root stress immediately compromises the tree’s ability to absorb water and nutrients. Furthermore, fire ants are known to tend populations of sap-sucking insects like aphids and scale for the sugary “honeydew” they excrete. This activity indirectly compounds the stress on the tree by increasing the presence of pests.
Protecting Vulnerable Trees and Treatment
The most effective strategy for managing fire ants near trees involves a two-pronged approach of prevention and targeted treatment. Property owners should regularly monitor the area around young or high-value trees for the characteristic dome-shaped mounds, especially in undisturbed soil areas near the trunk. Maintaining the tree’s health through proper watering and fertilization reduces overall stress, making the tree less susceptible to secondary damage. Physical barriers, such as a band of non-toxic sticky material applied to the trunk, can prevent the ants from climbing up to tend sap-sucking insects or chew the bark.
Eradication efforts should focus on methods that minimize chemical contact with the tree’s roots and trunk. The most recommended approach is the use of insecticidal baits, which the ants carry back to the colony, ultimately eliminating the queen. Baits containing active ingredients like hydramethylnon or indoxacarb are effective and pose a low risk to the tree when applied according to label instructions. For a direct mound treatment, a liquid drench can be used, but this must be applied carefully to saturate the entire nest without pooling near the trunk or causing excessive root disturbance.