Pests & Diseases FAQs

Argentine ants nest mainly in soil, retaining walls, and rock-gardens, under paths or cobblestones or at the base of plants in the warmer months. Wheelie bins and re-cycling containers, planter pots, cars and trucks also provide great nesting sites.

Some of the largest colonies have been found under the fake grass of tennis courts and around swimming pools.

Argentine ants are most active in dry, warm weather, but the onset of wet weather and cooler temperatures drives them into buildings. 

Over-wintering nests can contain hundreds of thousands of ants, and can usually be found inside the north or east facing warmer walls and in ceiling cavities.

The small satellite colonies established during the summer months can come together into huge colonies during the winter months, only to expand again into dispersed nests when the conditions become favourable.

Argentine ant workers are small (2-3mm) and a uniform honey-brown colour (most other common household ants in New Zealand are black).

Their size and colour is similar to some of our native ants. However, unlike native ants, Argentine ants will be found both inside and outside a house.

Unlike many household ants, Argentine ants prefer protein foods like meat in summer, when they are breeding (although they also enjoy sweet things like sugar or honey).

These ants move steadily in defined continuous trails that can often be seen climbing up trees or plants, especially if they are flowering. Native ant species don’t do this.

In places, these trails may be five or more ants wide. If you lay your hand across the trail, Argentine ants will frequently continue straight over and even investigate further up your arm. Most other ants would greet this blockage with confusion, taking some time to re-establish their pheromone trail-markers.

Argentine ants look similar to another pest species - Darwin’s ants – but can be distinguished from these by the ‘squash and sniff’ test. When squashed between the fingers, Darwin’s ants have a distinctive, formic odour; Argentine ants do not. Women are generally better at picking this smell than men.

Other ants commonly found around homes:

• White footed ants- Very common. Will eat most things but very attracted to sugar. They are shiny, give off a pungent odour when disturbed and form large nests in walls and ceilings of structures.
• Bigheaded ants- Red /brown, with two sizes of worker. The heads of major ants are noticeably large. They feed on cat food, dead insects and other protein sources.
• Black house ant- Very common, but only about half the size of the white-footed ant. Eats mainly sweet foods and builds large nests.                                                                                                     
• Forceps ant- Large and run around erratically; they look like they don’t know where they are going. They feed on animal food and are usually found in concrete paths, curbs or cobble-stones. They will bite and are a problem around BBQs and swimming pools.
• Darwin’s ant- Smaller than argentine ant (less than 2mm), but give off greasy odour when squashed. They have many of the same behavioural characteristics .i.e., soil nesting species, huge populations.

For more details on Argentine ant Identification visit:

http://www.landcareresearch.co.nz/research/biosecurity/stowaways/Ants/AAidentification.asp

Anything transported from point A to point B can potentially harbour Argentine ant nests.

Materials that are most at risk of harbouring a nest include rubbish, and garden or nursery products like potted plants, garden mulch, bark chips, and compost.

However, these ants also readily establish nests in cars, caravans, or even aircraft. And in this way can spread themselves across town, or around the country with ease.

Argentine ant infestations are frequently not detected until they have reached the stage of becoming a human nuisance. This may take two years or more. By the time they are detected, the ants are probably well established and may even have spawned sub-colonies that have hitched a lift elsewhere.

Argentine ants invade and colonise an area in two ways: budding and jump dispersal.

Budding

Unlike many other ants, Argentine ant queens do not go on nuptial flights, and so form new nests within ant-walking distance of the old nest. After mating, a young queen will simply walk away with some workers, and establish a new nest nearby. Left to themselves, colonies would increase by little more than 200 meters/year.

Jump dispersal

However, young queens will readily ‘bud off’ with a few workers and establish their nests in nearby vehicles, planter pots or wheelie bins. This done, they could end up anywhere.

This ability to ‘hitch’ a lift with humans makes the Argentine ant so challenging to control. And as these ants produce around ten times more queens than other species, the challenge is magnified.

Human-mediated dispersal within suburbs across a city, and between neighbouring towns is essentially creating a large number of small ant populations throughout New Zealand, and these are likely to act as centres for further expansion.

The Argentine ant has a wide dietary range and produces large numbers of aggressive and industrious workers.

They are one of a few ants species worldwide that have been identified as capable of invading native ecosystems and displacing native species, and because of this are listed as one of 100 of the world's worst invasive species by the Global Invasive Species Group, IUCN 

Argentine ants are omnivorous, with neighbouring colonies being genetically related. The relative lack of in-fighting between colonies makes the species highly competitive in the ant world.

When a colony has fully infiltrated an area, resulting in its complete dominance over other arthropod species, it has achieved ‘Super Colony’ status. The lack of other ant species and insects in the surrounding area is a clear indicator of this.

Super Colonies allow Argentine ants to form extensive, interconnected networks, not only through the suburbs of a town but even across vast distances.

In Mediterranean Europe, where Argentine ants have been established for many years, recent studies indicate the existence of a single, vast colony, stretching almost six thousand kilometres from Italy, through France, Spain and around the corner to Portugal.

New Zealand is particularly prone to the ecological impacts of exotic ants because our native flora and fauna has evolved without a large and ecologically dominant ant fauna.

Impacts on horticulture

Argentine ants can severely affect commercial horticulture by their tendency to nest in tree roots and by their farming and protecting honey dew producing insects (eg. aphids and scale insects). They hinder the growth of plants and trees and/or damage crops, and adversely affect pollination.

Pip fruit, stone fruit, subtropical fruit and cut flower crops are at medium risk; while olives, nuts, kiwi fruit  and  berry fruit  are  identified  as  medium-low  risk  crops.

New Zealand exports fruit to most countries, and these ants could affect our ability to comply with export requirements. The Argentine ant is not present in a number of Asian countries - for example China and Korea - and exporting goods contaminated with the ant to these countries could be detrimental to New Zealand’s trade image.

As these ants actively protect and tend sap-sucking insects, this could cause serious difficulties for organic growers who rely on biological control of their plant pests.

Lester, P.J.; Longson, C.G. 2002: Argentine ant distribution investigation: Horticultural areas. (7401 KB) Unpublished Victoria University of Wellington contract report for MAF Biosecurity Authority.

Impacts on biodiversity and ecosystems

The impacts of Argentine ants on both native invertebrates and vertebrates are well documented in Hawaii and California.

A recent study around Auckland has shown that open canopy habitats are most at risk of invasion, while forests are probably less susceptible.

Based on this, researchers suggest open habitats and relatively open scrub environments – including coastal conservation areas - in northern New Zealand are likely to be vulnerable to invasion by Argentine ants.

However they suggest that Argentine ants will not invade the interior of intact, closed-canopy indigenous forest.

“Harris, R. et al. 2002: A survey of the current distribution of Argentine ants, Linepithema humile, in native habitats in New Zealand, and assessment of future risk of establishment. Landcare Research Contract Report: LC0102/105 for MAF Biosecurity Authority. 

Urban impacts

The Argentine ant has already become a significant pest in some New Zealand urban areas,  persistently invading homes and commercial buildings in large numbers.

Overseas, in heavily infested areas residents are unable to live, relax or work comfortably inside or outside the home. On windy days the ants are blown off tree leaves onto people and their food. They constantly nip at exposed feet and legs in the garden and in the house, and trail into beds at night, disrupting sleep. Some people react to their bite.

Extreme measures have had to be taken by residents to prevent the ants entering bedrooms and beds, for example placing bed legs in pots of water; moving beds well away from walls and curtains, and ensuring sheets and blankets are tucked up off the floor.

Residents in affected areas report a  notable  absence  of  most  of  the  common  garden  insects  following  the establishment of the ants. They have also noticed reduced cropping of beans, peas and other home-grown vegetables.

On the other hand, affected residents find themselves fighting to control increased aphid and scale populations on citrus and ornamental shrubs (due to the ants nurturing these creatures), with some trees succumbing to the resulting stress and disease.

For more details on Argentine ant impacts visit the Landcare Research website  or read Potential impacts of the Argentine Ant (Linepithema humile) in New Zealand and options for its control.

Argentine ants were first detected as an established population in Auckland in1990. They have since spread quickly and are now present in many North Island cities and in two South Island locations.

http://www.landcareresearch.co.nz/research/biosecurity/stowaways/Ants/AAdistribution.asp

Argentine ants are often found closely associated with humans and human activities - e.g., in houses, gardens, plant nurseries and industrial areas. A recent study [WARD, ET AL .PDF] found human-mediated dispersal is primarily responsible for the spread of Argentine ants in New Zealand.

These ants hitch a ride in vehicles (including aircraft) and on transported materials of all kinds. They have the potential to spread throughout much of the North Island and northern South Island, as well as some South Island cities.

http://www.landcareresearch.co.nz/research/biosecurity/stowaways/Ants/AAfuturedistribution.asp

A single male Asian Tiger Mosquito was trapped at Shed 8 on the wharf at the Ports of Auckland on Friday 1st March 2007 as part of a routine mosquito surveillance program. Investigations are currently underway to establish whether this is a one off event or whether it is part of a localised population.

The Asian Tiger Mosquito (Aedes albopictus) occurs throughout the tropics of Southeast Asia, the Northern Pacific and Indian Ocean Islands, north through China and Japan and west to Madagascar. The Mosquito has also spread to North and South America, with more recent introductions into areas within Africa, Australia, the South Pacific Islands and Europe.

Mosquitoes go through four separate and distinct stages during their life cycle: eggs, larvae, pupae (resting stage), and adults. They have an elongated proboscis (mouth piece) with which the female bites and feeds on blood.

Our mosquito identification experts use microscopes to identify physical differences to tell different species apart.

Adult Asian Tiger Mosquitoes range in size of approximately 2 mm to 10 mm and have black bodies with a conspicuous pattern of white stripes. There is a distinctive single white band (stripe) down the length of the back. There is also a native New Zealand mosquito that has white stripes, so the best indication of an Asian Tiger mosquito may be aggressive daytime biting. Adult female Asian Tiger Mosquitoes feed on humans, animals, birds and frogs.

MAF Biosecurity New Zealand is encouraging members of the public in the Ports of Auckland/downtown Auckland area to report unusual mosquito activity. Unusual activity means aggressive daytime biting, usually in shaded outdoor areas. If possible collect a sample by placing it in a sealed container and report your find to the Ministry of Health’s hotline 0800 MOZZIE (0800 669943).

If you are concerned about mosquitoes you can avoid being bitten when outdoors by wearing a repellent cream or spray preferably containing DEET (diethyl toluamide) and wearing light-coloured protective clothing such as long sleeved shirts, long pants and hats to minimise skin exposure.