Ants are one of the major subgroups of the insect order Hymenoptera, which also includes wasps and bees. Most species are distinguished by one or two small segments that separate the middle of the body (mesosoma) from the main part of the abdomen (gaster).
There are about 15,000 described species worldwide. Most of the world’s ants are found in moist, warm habitats.
There are four stages in the life cycle: egg, larva, pupa, and adult. The cycle usually lasts from six to 10 weeks. Some queen ants can live for up to 29 years, and some workers for up to seven years. Males usually live only a few weeks, and die shortly after their mating flight.
Ants are social insects, living in colonies ranging from around 100 in the case of New Zealand’s ancient Amblyopone species, to well over a million for the introduced Argentine ant Linepithema humile.
A colony consists of queens, males and workers (wingless females). The males have wings and fly in swarms with young queens. Once they have mated, the queens drop to the ground. They chew or break off their wings, and dig a small hole where they lay their eggs and start a colony.
Fertilised eggs produce female ants – queens and workers. Unfertilised eggs produce male ants.
Ants are mainly scavengers and general predators, eating fats, sugars, oils and protein. Solid food is carried back to the colony for the larvae. However, adult ants feed only on liquids taken from their prey (which includes living and dead invertebrates), from sap-sucking bugs and from plant glands.
Some species have a strong preference for sweet foods while others, like the large-headed Pheidole species, prefer fatty and oily foods.
One native New Zealand species, Discothyrea antarctica – like other Discothyrea species – probably preys specifically on the eggs of arthropods (insects, spiders and the like).
The introduced Australian ants Orectognathus antennatus and Strumigenys perplexa have long, projecting jaws that act like spring-traps. These ants eat springtails (primitive insects of the genus Collembola) and small, soft-bodied soil animals.
Queens and workers may have a sting to defend themselves and subdue prey, or a ‘spray nozzle’ through which they squirt formic acid. Depending on the species, the sting can be mild to very painful. Some will bite as well.
New Zealand has only 11 known species of ant, probably in part because of its cooler, temperate climate. (In comparison, Australia has about 1,200 described species and an estimated total of twice that number.) Surprisingly little is known about some native ants, and further research may reveal more species.
As a group New Zealand’s ants are less diverse and aggressive than ants on many other land masses. The absence of aggressive ants could have been a factor in the evolution of a rich range of invertebrates in the soil and leaf litter of New Zealand’s native forests.
Māori have many words for ant, including pokorua, pokopokorua, pōpokorua, pōpokoriki, nonoko, rōroro, torotoro and upokorua.
Torotoro is a northern Māori name for an ant. The word also means scouting or exploring, and may refer to the way ants set off from their colony in search of food. Plant runners are also called torotoro. A rātā vine, with long slender stems climbing up the side of its host tree, is called aka torotoro.
Most of New Zealand’s ant species occur all around the country, mainly in forest.
The southern ant (Monomorium antarcticum) is the most common. This species shows a lot of variation, and it is uncertain whether it is a single species or a complex of several species.
Workers are about 3–4 millimetres long, and can range in colour from orange with darker markings to entirely black. They live in almost all habitats: forest, grassland, dry river beds, sphagnum bogs, rotting logs, and suburban gardens and lawns. They also forage along the shore or high in the mountains. This species is known to gather and store plant seeds. Nests range from small to well populated, with thousands of workers.
Named for the swirls on its head and body, the striated ant (Huberia striata) is slightly larger than the southern ant, and workers range from reddish yellow to black. This one is also abundant and lives in similar habitats to the southern ant.
In some nests, a large number of shells of a small native land snail have been found. It is thought that the ants capture live snails and bring them into the nest, where they feed on them. The colonies can hold hundreds of thousands of workers.
Both the southern and striated ants are found in close association with sap-sucking bugs (some species of the insect suborder Homoptera), which they milk for their sweet excreta.
The largest native ants are Pachycondyla castanea and P. castaneicolor, the biggest workers of which are over 6 millimetres long. These reddish brown ants have a strong sting. While more at home in native bush and forest, they have also been found in urban areas.
The native ant Amblyopone saundersi and the closely related, introduced Australian Amblyopone australis are rather sluggish ants, which make only small nests of up to a few hundred individuals. They hunt underground or in enclosed spaces such as rotting wood and leaf litter.
They sting to paralyse or kill insects and other arthropods, and feed the partially dismembered bodies to their larvae. While they can inflict a painful sting on humans, they are not aggressive.
New Zealand has about 28 foreign species of ant, which have become established mostly through accidental human transport. The majority have come from Australia. Others are invasive species that have colonised many countries. Several are bothersome pests around the house, and some have the potential to invade native habitats, which would have a severe impact on native species and ecosystems. Most are found in the warmer parts of the North Island.
Because ants can be easily carried around the world with cargo on planes and ships, the Ministry of Agriculture and Forestry established a national invasive ant surveillance programme in 2001. This monitors the points of entry to New Zealand, particularly ports.
The most common introduced ant is the white-footed house ant (Technomyrmex jocsus). It often nests in walls and forages in houses for water and food, particularly sweet items. This ant also protects plant pests such as scale insects and mealybugs, in order to feed on the honeydew they produce.
The colonies have several thousand workers and many functional queens, so their numbers can build rapidly.
The Argentine ant (Linepithema humile) is one of the world’s 100 most invasive species. This light brown ant (2.2–2.6 millimetres long) is well established in much of the North Island and parts of the South Island. It thrives in open areas and bush with open canopy, but does not penetrate far into native forest.
An invasive ant known as the red imported fire ant (Solenopsis invicta) is spreading around the world. It has been found and eradicated on three occasions in New Zealand. In some parts of the USA and Queensland it’s impossible to walk or sit on the grass because the ants swarm from their underground nests when disturbed, and attack and sting anything nearby. The sting is as painful as a bee sting, and produces a pustule on the skin.
Argentine ants form super-colonies with many queens, and displace other ant species. Competitive, and eating a broad range of food, they could have far-reaching effects on natural ecosystems, as they have in other countries. The Department of Conservation established an eradication programme on the wildlife reserve island of Tiritiri Matangi in the Hauraki Gulf, but colonies on the mainland present a greater challenge.
In urban areas the Argentine ant is a pest because it forages indoors, swarms over pot plants and feeds on honeydew produced by mealybugs and scale insects – plant pests that they protect from predation. They swarm up your arms and legs if you disturb their nest. They bite, but they cannot sting.
Don, Warwick. Ants of New Zealand. Dunedin: Otago University Press, 2007.
Hölldobler, Bert, and Edward O. Wilson. The ants. Cambridge: Bellknap, 1990.