Odorous House Ant

Tapinoma sessile — the odorous house ant — is one of the most common indoor ant species in North America and the source of the distinctive 'rotten coconut' or 'blue cheese' smell that emanates when the ants are crushed. The defensive secretion (from a thoracic gland) is a pyrazine-and-methyl-ketone cocktail that smells strikingly similar to the volatile organic compounds released by spoiling coconut and certain blue cheeses. Workers are 2-3 mm long, dark brown to black, and form trails of foraging columns indoors and outdoors. Colonies vary from small single-queen single-nest units of a few hundred workers to massive supercolonies with hundreds of queens, hundreds of thousands of workers, and multiple interconnected nest sites. The species' invasion biology defeats traditional pest control: like pharaoh ants, odorous house ants 'bud' when stressed — workers and brood fragments split off to establish new satellite colonies, often making infestations worse after spray treatment. The only effective control is slow-acting bait that workers carry back to the queens. The species is native to North America (a refreshing change from the many invasive ants in residential pest control) and ranges from Canada to northern Mexico. Indoor infestations spike in spring and after heavy rains, when outdoor colonies migrate into wall voids, behind cabinets, and around plumbing.