Argentine ants (Iridomyrmex humilis) have a one-segmented petiole, an uneven thorax when viewed from the side, lack a ring of hairs at the tip of the abdomen and are sting-less. Their antenna are 12-segmented with the long first segment about the same length as the head. The workers are monomorphic and are about 2.2 to 2.6 mm long. Its thought that the Argentine ant made its way into the United States at New Orleans on coffee ships from Brazil in the 1800's, and since these ants are readily transported by human activity, they have spread throughout the country very quickly. Their nests can contain many queens, and new colonies are often formed when inseminated queens walk off to new locations followed by a number of workers.