Thief Ant

Thief ants are among the smallest structural pest ants, pale yellow to light brown workers just 1.5–2 mm long with a two-segmented waist and, diagnostically, 10-segmented antennae ending in a distinct two-segmented club. Colonies are polygynous with several hundred to several thousand workers, and their tiny size lets them exploit spaces other ants cannot reach. Mating flights occur in mid to late summer, though established indoor colonies persist year-round in heated buildings.

The common name comes from their habit of nesting immediately adjacent to — sometimes inside the walls of — larger ant and termite colonies and stealing brood and food from them. Unlike most household ants, they strongly prefer greasy and protein foods over sweets: meats, cheese, nuts, oils, and pet food, which is why sweet-only bait programmes fail against them. They are readily overlooked because of their size and their very thin, slow trails, and they are a documented contaminant of packaged food.