Thatching ants (Formica genus) are common pests, most noticeable due to the distinctive mounds they construct in lawns and open areas. While they can be beneficial by preying on other insects, their mound-building activities can damage turf and plant roots. These large, established colonies require a targeted strategy that goes beyond simple surface treatment to achieve lasting removal. The following steps detail how to identify this pest and implement effective non-chemical, chemical, and preventative measures to manage their presence.
How to Identify Thatching Ants and Their Mounds
Thatching ants are medium to large, ranging from 4 to 8 millimeters in length. Workers display a bi-colored appearance, featuring a reddish-orange head and thorax with a black abdomen. A distinguishing feature is a subtle notch or depression on the top of the ant’s thorax, which helps differentiate them from carpenter ants.
Their nests are the most obvious sign of an infestation, presenting as large, cone-shaped mounds built from organic debris like grass stems, pine needles, and soil particles. This “thatch” layer can be substantial, sometimes reaching over a meter across, and helps regulate the temperature and humidity of the subterranean nest. The mounds often have multiple entrances and are found in sunny, open areas, though the nest tunnels extend several feet into the ground.
Non-Chemical and Physical Removal Techniques
Physical removal and natural treatments offer initial control methods for those seeking to avoid synthetic pesticides. One technique involves carefully excavating the mound and the underground portion of the nest, which can extend up to four feet deep, to relocate the entire colony. Due to the size and aggressive nature of the ants, this method is often best performed by professionals using heavy equipment to ensure the queen and all satellite nests are removed.
Applying boiling water directly into the mound’s core is another method, though it must be used with caution to avoid scalding nearby plants and turf. This approach aims to kill the queen and a significant portion of the colony instantly. However, it is rarely effective for large, deep nests and requires penetrating the protective thatch layer.
A less destructive option is the application of food-grade diatomaceous earth (DE). This naturally occurring powder works by physically absorbing the protective wax layer from the ants’ exoskeletons, leading to fatal dehydration. The powder should be dusted directly onto active mound entrances and trails, where foraging ants will carry it into the colony, extending its effect to other ants within the nest.
Choosing the Right Chemical Treatment
Effective chemical control requires eliminating the deep-seated colony, not just the surface workers. Contact treatments, such as liquid insecticides containing active ingredients like cypermethrin or cyfluthrin, are applied directly to the nest. This method is most effective when the mound is first penetrated and agitated with a shovel to expose the subterranean galleries, allowing the product to reach the queen and brood. Treating only the visible entrance holes will prompt the colony to relocate or create a new entrance nearby.
Baiting offers a slower, more thorough method for colony elimination by leveraging the ants’ foraging behavior. Baits, available in granular or gel formulations, contain a slow-acting poison, such as boric acid or fipronil, mixed with an attractant food source. Worker ants carry the bait back to the nest, sharing it with the queen and larvae through trophallaxis, which gradually poisons the entire colony over several days or weeks.
It is recommended to use a non-repellent liquid insecticide for direct mound treatment, as this product is undetectable to the ants, allowing them to transfer the chemical to other colony members. When applying any product, select one specifically labeled for Formica species and follow the manufacturer’s application instructions precisely. If the infestation involves multiple large mounds or is located in a sensitive area, consulting a licensed pest control professional is the most reliable course of action.
Long-Term Prevention and Maintenance Strategies
Preventing colony re-establishment involves making the surrounding environment less hospitable for nest construction. Since these ants build their mounds from organic materials, regularly removing debris like fallen branches, leaf piles, and yard clippings eliminates their primary building supplies. Keeping firewood stacked away from the home and removing decaying wood from the property will also discourage nesting.
Cultural controls, such as maintaining a well-groomed lawn and improving soil drainage, reduce conditions attractive to colony development. Sealing all cracks and crevices in the foundation and around utility entry points with caulk is necessary if ants attempt to enter a structure. Applying a perimeter barrier treatment, typically a granular or liquid insecticide, around the home’s foundation can deter foraging ants from establishing new nests.