There are 40 confirmed species of ants in New Zealand. Of these, only 11 are endemic (found only in New Zealand), which are generally widespread geographically and commonly found in forested habitats. The other 29 are introduced species, accidentally transported to New Zealand by humans, mostly from Australia. Ants thrive in most ecosystems and may form 15–25% of the terrestrial animal biomass. Their success in so many environments has been attributed to their social organisation and their ability to modify habitats, tap resources, and defend themselves. Ant societies have a division of labour, communication between individuals, and an ability to solve complex problems.
Usually, they are not a house pest but can become a considerable nuisance pest if they enter houses in search of food or shelter. They are also important from a biodiversity point of view e.g. red imported fire ant (Solenopsis invicta), is regarded as invasive species, establishing themselves in areas where they have been introduced accidentally. Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies that may occupy large territories and consist of millions of individuals. Nearly all ant colonies also have some fertile males called “drones” and one or more fertile females called “queens”.
Identification features of Ants:
Clubbed or bent antennae
When wings are present, the front wings will be longer than the back wings on ants
Some ant species
have a stinger at the end of the abdomen
The most important species found as pests in New Zealand are:
White footed ants (WFA) are medium small (3mm long), jet black in colour, with pale legs, one segmented waist and proportionally larger pointed gasters (abdomens) with no sting. They form multi- nest and can have multi-queens.
They are usually nocturnal, and seem to favour kitchens and bathrooms, but in cold climates can be found nesting in electrical appliances, circuit-boards etc., often causing the malfunctioning or destruction of these tools. Many foragers come out of their nests to search for new food resources. Often the same trails (4-5 ants wide) are observed between a nest and resource for months at a time. In and on structures, foragers tend to follow lines.
Habitat and Food: They are found throughout New Zealand both indoor (kitchen and bathroom) and outdoor (trial on walls) but more prevalent in warmer areas. They are strongly attracted to sweet foods. They also feed on dead insects and other protein. WFAs are commonly found foraging along branches and trunks of trees and shrubs that have nectars and/or sap-sucking insects that produce honeydew.
Risks: Do not sting. Seen more as a nuisance rather than a pest, these ants are troublesome because of their large colonies and constant foraging in kitchens, bathrooms and the exteriors of buildings.
Distinguishing Feature: Pale yellowish to white feet (tarsi).
Note: The WFA is sometimes mistaken for Argentine ant, Linepithema humile (Mayr) and black house ant Ochetellus glaber. However, their petiole has a vertical projection which is lacking on the WFA. This small
ant is also easily confused with crazy ants but its legs and first segment of its antennae are much shorter than crazy ants.
The black house ants are 2.5 mm to 3 mm long intensely black ants found in both urban and rural areas. They are little smaller and stockier than the White-footed house ants and more intensely black, with a sometimes subtle, but distinct, purplish blue-green iridescence. They have single nest and only one queen per colony. They form conspicuous files on tree trunks in their search for honeydew and small insects, having often been seen trailing into holes in trees, fence posts and flax flower stems. Black Ants can be a pest around homes, especially when they get into the kitchen.
Distinguishing Features: This ant has a prominent node (petiole), which is a distinguishing feature from the white-footed house ant.
Habitat and food: It often nests arboreally, under stones, or in dry fallen logs. It nests around houses against paths, stones or dry logs, cracks and crevices. Occasionally in wall cavities and roof voids. When they are nesting in the house they can sometimes be detected by the mess of black droppings on floors or windowsills. Black Ants eat mostly sweet foods but they are omnivorous, feeding on insects and worms, as well as vegetation, such as small seeds.
Risks: Do not sting. But these ants are regarded as a nuisance and scavenge in kitchens, garbage and also dog excrement,
therefore potentially spreading diseases such as salmonella.
Argentine ants are about 2mm to 3mm, dark to medium brown ants with smooth shiny bodies. They are very aggressive and combined with their large colonies can dominate other species that share their habitat. Once they have established in an area they are very aggressive and competitive, threatening native invertebrates, nesting birds and horticultural enterprises. As such they have been listed by the World Conservation Union as one of the world’s 100 worst invasive specie. They have multi-nests and have multi-queens. The females mate in their nest so no swarming is seen. Argentine ants are highly active in searching for food and their trails are often five or more ants wide. They walk in defined continuous trails (not erratic ‘crazy’ behaviour of running about in circles). They invade houses and are capable of penetrating food containers. They follow food trails for long distances so nests are not easy to track. Unlike most other ants, they climb trees to get to food sources.
Habitat and food:Linepithema humile is found in many habitats including forests, grasslands, river catchments, shrublands, farmland, coastland, urban areas and wetlands. Also under paving and in wall cavities. Preferably they feed on sweet foods such as the honeydew produced by aphids, scale insects and mealybugs but also go for proteins and oil. They are both indoors and outdoors pests
Distinguishing Features: Head is teardrop shaped with the relatively low placement of the eyes. The widest point of head above eyes. Eyes, in full face view, do not break outline of head. Argentine ants don’t smell when squashed. Argentine ants drive out other ant species from an area. Travel steadily in defined continuous trails up to five or six ants (or 2 cm) wide and travel up trees and buildings.
Risks: No sting but they are aggressive so may bite.
The Anoplolepis gracilipes is 1- 5mm, brownish-yellow with darker abdomen (sometimes with light brown bands). It is commonly known as the yellow crazy ant because of its colour and frantic erratic behaviour (“crazy”) when disturbed. Like many other ants this is a “tramp ant” (a species that easily becomes established and dominant in new habitat due to traits such as aggression toward other ant species, little aggression toward members of its own species, efficient recruitment, and large colony size). Also known as the long-legged ant or Maldive ant, it is on a list of “One Hundred of the World’s Worst Invasive Alien Species” formulated by the International Union for Conservation of Nature (IUCN).
Yellow crazy ant’s exhibit uni-colonial behaviour (cooperation and lack of aggressive behaviour between the foraging ants of multiple colonies, each with their own queen) and can form multiple large high-density super-colonies. Yellow crazy ants forage day and night, generally when temperatures are 21–35 ˚C, but most intensely at dusk, when humidity and temperature are relatively high. Unlike some ant species, use of conspicuous foraging trails is not common.
Habitat and food: Yellow crazy ants usually nest in areas with access to moisture such as along creek banks, under logs or piles of timber, around base of trees, amongst debris or leaf litter, within retaining walls. A. gracilipes are an outdoor pest and has been described as a “scavenging predator”. It has a broad diet, a characteristic of many invasive species. It consumes a wide variety of foods including grains, seeds, arthropods, and decaying matter, including vertebrate corpses.
Distinguishing Features: Fast, erratic moving ant, with long legs about 5mm long, large eyes and extremely long antennal scapes (the legs and antennae are very long in proportion to the body). It has a single waist segment—the petiole—which is thick and raised.
This ant may be confused with the Weaver Ant (Oecophylla smaragdina), which is much larger in size and extremely ferocious. Yellow Crazy Ant does not bite or at least its jaw is not able to cause harm to humans. Conversely, the bite from the Weaver Ant is painful. In addition, the nest of the Yellow Crazy Ant is on the ground while that of the Weaver Ant is constructed with leaves on plants. They also may be distinguished from other ants, like the Argentine ant, by the many hairs on their body, including four pairs of hairs on the top of their thorax. Crazy ants are also quite different in the sense that they don’t have flying queens
Risks: Crazy ants do not bite but spray formic acid to subdue prey, this can irritate skin and eyes of people coming in contact with the ants.
Prevention and Control
Clean up food scraps, spilled sugar, and fat in food preparation & mess areas.
Keep sugary foods in containers with tight-fitting lids.
Keep outdoor rubbish areas free of food scraps.
do not plant plants close to walls that attract ants especially those plants that get whitefly and aphid These insects secrete honeydew which is the main source of attraction and food for ants around houses to start with and over a period of time as their population grows they start entering homes and becomes a nuisance.
Seal cracks around foundations drain etc.
Tip hot water over ant trails and into cracks in paths from which they emerge (it dilutes their chemical trail).
Apply a contact insecticide such as Hawkeye spider and insect spray around areas where ants are a nuisance and around entry points, particularly around drains, doorways, steps, and foundations.
Apply slow-acting bait such as Hawkeye Ant bait at sites where ants feed. This will be taken back to the nest where it will kill most of the adults and young ones wiping out the whole nest.