Argentine Ants

(Linepithema humile)

Containment Pest

Argentine Ants were first recorded as established in New Zealand in 1990 in Auckland. Since then, Argentine Ants have spread rapidly throughout the North Island and into Nelson and Christchurch. They were first recorded at Port Nelson in 2001 and controlled but not eliminated. The wingless worker ant, the one most commonly seen, is light to dark honey-brown in colour and 2–3 millimetres long; most other common household ants are black. Argentine Ants move very quickly and move along trails five or more ants wide when searching for food; they can lead up trees or buildings. If an Argentine Ant is squashed, there is no strong formic acid smell as there is with some ants (eg, Darwin’s Ants).

Reasons for the StrategyClose up shot of an Argentine ant

Argentine Ants are easily spread by human-related activities (eg, movement of pot plants, vehicles, etc). Argentine Ants rank highly as a domestic nuisance species. They invade houses and are capable of penetrating food containers. They infest gardens, making outdoor dining difficult. When nests are disturbed, foraging ants will run up legs and arms, and some people are sensitive to their bite. Argentine Ants have the potential to spread disease around buildings, including hospitals, and are pests in rest homes. Argentine Ants also negatively impact on invertebrate communities through predation, competition, and interference. Ecosystem processes, such as soil formation and decomposition, are likely to be negatively affected.

Argentine Ants feed extensively on the honeydew produced by sap-sucking bugs, such as aphids and scale insects, and actively disperse them and protect them from predation. This can increase the number of introduced sap-sucking bugs in native habitats and in domestic and commercial orchards, interfere with predators of sap-sucking bugs, and aid transmission of diseases between plants. There are numerous potential impacts of Argentine Ants on the commercial sector in urban environments; including ants invading food processing plants and becoming important pests of the hospitality industry. Argentine Ants have been found predominantly in urban areas and on the margins of native habitats. There is concern about their spread into coastal shrublands, especially in areas like Abel Tasman National Park. Their potential impact on native ecosystems in New Zealand remains largely unknown. The development and manufacture of an ant bait has made it possible for land occupiers to reduce ant numbers to very low levels, but eradication seems impossible to achieve in urban or industrial settings.

Argentine Ants are assessed at “4” on the infestation curve. Extensive areas of suitable habitat, and the potential for them to cause significant adverse effects, mean the benefits of containment control far outweigh the costs.

Objective

To address the adverse effects of Argentine Ants during the term of the Strategy by:

  • Containing Argentine Ants in the infested urban areas.
  • Keeping uninfested areas clear of Argentine Ants.

Alternative Measures

The alternative option of “do nothing” or relying on voluntary control will not achieve the objective of containing Argentine Ants, and will result in significant additional costs to the community with respect to lost production and natural values, and the increased cost of control in the future.

Strategy Rule for Argentine Ants

  1. The occupier of Argentine Ant-infested land shall bait to control Argentine Ants.
  2. The occupier shall take all reasonable precautions to prevent the spread of Argentine Ants in rubbish, pot plants, equipment and vehicles.

A breach of Strategy Rule 6.1.5 is an offence under Section 154(r) of the Biosecurity Act 1993.

Biosecurity Act Requirement

No person shall knowingly sell, propagate, breed, release, or commercially display Argentine Ants, under Sections 52 and 53 of the Act.

How to identify Argentine ants

The two main ways to identify the ants are by their colour and their trails. The worker ant, which is the most commonly seen, is light to dark honey brown and around 2-3mm long, which means they are slightly smaller and a lighter colour than New Zealand's common black household ant.

Argentine ants tend to travel in numbers; their trails are often five or more ants wide and travel up trees or buildings. Other species don't tend to climb trees or have such obvious trails, unless they are moving their nest, in which case the ants would be carrying their eggs. If you place your finger on the ground in front of an ant, its behaviour should indicate whether it is an Argentine ant or not. While other ants will move away from your finger, Argentine ants will approach your finger and try to climb it.

The ants are not poisonous but they are aggressive and do bite. They have a tendency to displace all other insects inside the area affected by the colony, except for aphids and scale insects on plants, which they farm to produce honey dew. The colonies of Argentine ants are interconnected and co-operative; their sheer numbers gives them a competitive edge against other insect populations. So if you have other ant species on your property then it is unlikely that you will have Argentine ants.

If you need assistance identifying Argentine ants, please contact Tasman District Council on +64 3 543 8400. Nelson City Council contracts pest management services out to Tasman District Council.


Download Tasman District Council's Argentine and Darwin Ants information brochure. (261KB PDF)

Why they are a problem

  • Argentine ants multiply very quickly.
  • They have a huge appetite, and utilise any food source they can find.
  • They can quickly overrun your property, making it almost impossible for you to enjoy your outdoor areas.
  • Indoors, they are a serious pest. They can get into your food sources, including screw top jars, microwaves and fridges.
  • People in Nelson are finding them in their bedrooms, toilets, and kitchens.
  • Argentine ants can bite (although they aren’t poisonous).
  • Argentine ants can completely eliminate other types of ants and destroy beneficial insects and earthworms.
  • Argentine ants can kill baby birds in the nest.
    Argentine ants will cause an increase of aphids and scale insects, on your property.
  • Argentine ants damage fruit-bearing trees and plants.
  • If left unchecked, Argentine ants can become a serious threat to viticulture, flowers, avocado, tomato and citrus crops. They are a particular threat to organic gardeners.

What to do if you suspect you have Argentine ants

Call a pest control operator (check the Yellow pages) or Biosecurity Officers at Tasman District Council (TDC) can help with identifying Argentine ants. Use a dollop of peanut butter and jam as bait to attract suffient number of ants. Scoop them into a container with a tightly-sealing lid. Label container with your name, property address and phone number. Bring it to the TDC office (189 Queen Street, Richmond) or the NCC office (110 Trafalgar Street, Nelson).

Please note

Argentine ants should not be attacked at the wrong time or with standard household insect poisons as it could instigate a breeding cycle, making the problem worse.

If you have Argentine ants inside, or if they are a problem in your outside area, do not

  • try to eradicate them using conventional methods.
  • use petrol, kerosene, or other substances. Using these flammable substances may also invalidate your homeowners insurance.

The ants are not a health risk, however, as the weather warms, the ants will become more active and therefore more noticeable.

Control indoors

Keep food tightly sealed, wipe bench tops will diluted lemon juice or vinegar.

So your family don't get bitten at night - Move beds away from walls, keep sheets and blankets up off the floor.

Control outdoors

When gardening, cover up any disturbed nest until able to treat it.

Cut back vegetation growing against the side of your house, and spray affected trees for scale insects and aphids.

Don't leave food scraps lying on the ground, particularly near your house

To prevent the ants spreading to other parts of Nelson

Don't share your pot plants, compost, top soil or bark with anyone - keep it on your property until well after the eradication is complete. If you employ contract gardeners, remind them that any waste they remove from your property is risky.

When friends visit, make sure they park their car with the wheels NOT touching the kerb, where the ants may be running- leave a gap so the ants can't get on to their car wheels; make sure they don't park underneath or touching any vegetation.

If you have a motor home or caravan sitting outside on your property and you want to drive it outside the area, please check the wheels and underside for any infestation as this is one of the main ways the ants are spread.

Treatment options

Find out about control methods for Argentine Ant infestation on  Tasman District Council's control methods page.