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Darwin's ant worker ants are about 2 mm long. They have a dark-brown head but the rest of the body and the legs are light brown. They look similar to Argentine ants but they give off a strong odour when crushed, which Argentine ants don't.
Darwin's ants are native to Australia, where they are most commonly found in dry forested areas, including coastal scrub or heath, nesting in soil, under rocks or rotten logs, or occasionally in abandoned nests of other ants. Nests usually contain several hundred workers which disperse quickly when disturbed. In New Zealand, the species is associated with towns or cities with ports. It has been recorded in Whangarei, Mt Maunganui, Gisborne, Napier, Blenheim, Nelson and Lyttelton.
Several biological factors ensure the success of Argentine ants. These include: multi-queened colonies; large numbers of offspring and rapid recruitment; a very general diet and an ability to monopolise food sources; an ability to exploit a diversity of habitats; a propensity for forming super-colonies through successful mixing of individuals from separate nests that are linked by foraging trails and aggression to other ants. Their aggression and numerical dominance enables them to displace other ant species. The World Conservation Union lists the Argentine ant as one of the world´s worst invasive species.
Darwin's ants can also build up large densities, often in urban gardens becoming a nuisance and displacing other invertebrates. Darwin's ants nest in soil or under stones and logs and usually maintain small colony sizes.
If you suspect you have Darwins ants you can get them identified by delivering a sample to a Northland Regional Council office. Ant samples should be put into a screw-top container and frozen.
Ensure soil potted plants, outdoor equipment or other mediums which could contain ants are ant-free before moving these to other areas.