Argentine ants are small (2.5-3mm) brown ants with a single node in the waist. They are typically found travelling in well defined trails between nests and food sources. Unlike other common small brown ant species, such as the coastal brown ant, Pheidole megacephala (Fabricius), Argentine ants do not have a soldier caste, so all the individuals out scavenging for food are the same size.

The eggs of Argentine ants are elliptical in outline, pearly-white in colour, and take from 12 days to nearly 2 months to hatch. The larval stage may be completed in from 11 to 60 days. The pupal period may extend over 10 to 25 days. The minimum period from egg to adult is about 1 month but it may be 4 to 5 months and averages 2-3 months.

The population of a colony may vary from a dozen to many thousands and the number of queens from one to hundreds. During the warmer months, satellite nests are usually established close to food sources and these satellite nests are highly mobile, with the workers moving in with eggs and larvae over a short period and abandoning the nest if it is disturbed or the food used up. The adult winged males, which are larger than the workers but much smaller than the winged queens, usually fertilise the queens in the nest and the new queens establish nests nearby after losing their wings.

Argentine ants become a major domestic pest by invading houses and swarming over foodstuffs, including entering fridges, unopened packets and have even been known to follow the spiral down inside screw-top jars to get at the contents, particularly if the contents are sweet. They invade beds at night seeking moisture and can swarm over sleeping babies, although they are not known to do any damage.

Unlike many other domestic pest species, Argentine ants do not nest in houses but nest outside and enter houses in dense trails which can resemble miniature multi-lane highways.