Ants that are referred to as “tramp ants” are pest species that have colonized a variety of different habitats all over the world. The most commonly encountered tramp ant species in the northeast include Pharaoh ants and crazy ants, and everyone has likely encountered indoor tramp ants at some point. In addition to their wide global distribution, tramp ants have also adapted to living within human dwellings where they seek out human food sources. Unsurprisingly, researchers have been unable to conclusively determine where many tramp ant species originate in the world, as most tramp ants have become fully integrated with the ecosystems that they have invaded. One of these species, the odorous house ant, is frequently labeled a tramp ant and a North American native by the same sources. This is likely due to this species’ varying status as a household pest. Up until 20 years ago, odorous house ants were not considered major household pests, but for reasons that are not yet understood, this species’ pest behavior changed dramatically. For example, during the late 1990s, researchers in the northeast began to notice that local odorous house ants were infesting a greater number and variety of structures, and their colonies grew dramatically, making these ants very difficult to eradicate from infested homes.

One theory that has been put forth concerning the odorous house ant’s change in pest behavior states that odorous house ant infestations have increased due to the growing popularity of residential landscaping. This theory has not been thoroughly studied, but it is not unfounded, as odorous house ants have been found in brand new bags of mulch, and pest control professionals have noticed an increase in odorous house ants nesting with mulch at the homes they visit. One pest control professional claimed that he had found a dozen odorous house ant nests within garden mulch surrounding a home’s foundation. The mulch had just been laid by the homeowner along with an abundance of ornamental vegetation, but when the area’s soil was dry and free of plants, not a single ant was found around the home’s foundation. In this situation, odorous house ants were likely abundant on the homeowner’s lawn, but after the mulch was laid and the plants were installed around the foundation, the ants migrated onto the garden bed in order to dwell in moist soil. Since odorous house ants prefer moist habitats where damp soil and plant matter are abundant, they naturally moved onto the garden bed, as the mulch and vegetation acted as a barrier that prevents moisture in the soil from evaporating. This is why odorous house ants often infest homes that are located on landscaped properties. Placing landscaping ornaments, and an overabundance of mulch and/or vegetation too close to a home’s foundation may see odorous house ants invade the home through cracks in the foundation. Keeping mulch and vegetation a foot or more away from a home’s foundation will help keep these ants out of homes.

Have you ever encountered an abundance of pests around your home’s foundation?