Invasive Ants

What are Invasive Ants?

Invasive Ants are those which are able to build up in number quickly and dominate areas, displacing other Ants and insects and aggressively occupying large areas. We have a lot of native Ant species in New Zealand as well as a few introduced ants that, while being a nuisance in the home (for example the Black House Ant), are not considered an environmental pest. There are a number of Invasive Ant species that have established or have tried to establish in New Zealand; two main Invasive Ants that are within the region is the Darwin Ant and Argentine Ant. Argentine Ants are particularly aggressive Ants which will kill other insects and even kill lizards and birds. They also have the capability to harvest sugar-exuding insects, for example they will protect aphids from predators so they can harvest the sugar that is naturally excreted from the aphids.

How are Ants Spread?

Generally Ants are able to spread to new areas by hitching a ride on materials that we move around, for example, potting mix, plants, gravel and other landscaping materials. Care should be taken when buying landscaping materials and potted plants (from both shops and privately) that you are not also taking home a nest of Ants.

Where are Darwin and Argentine Ants Found?

Through surveillance, Council has found Darwin Ants very widespread in Marlborough and can be found in Picton, Blenheim, Havelock and surrounding areas.

It was thought that Argentine Ants had a limited distribution in Marlborough, but surveillance has shown it is also a lot more widespread than first thought, and is found in big patches through both Picton and Blenheim.

Both of these Ants are patchily spread through the North Island (particularly Auckland and Northland), Top of the South and Christchurch. Because these Ants are hitchhikers they are found in most areas where there are ports and main trunk lines.

What Do Darwin and Argentine Look Like?

Darwin Ants are fawn brown in colour and about the same size as the commonly known black house ant. The big difference between Darwin Ants and other ants is a strong odour (similar to nail polish) when squashed.

Argentine Ants are also fawn brown in colour and slightly bigger than the Darwin Ant. They are aggressive and if a log is knocked, masses of Ants will appear to protect their territory. Argentine Ants often form large colonies quickly and can be seen forming routes to food sources that are two or three Ants wide. Overseas, Argentine Ants can form nesting colonies that are 5km in length, but this has not been seen in New Zealand.

Go to the Landcare Research website for more information on Argentine Ants

How Do I Control Ants?

There are two main methods to controlling Ants which should be used in conjunction with each other for best results: spray/sand/dust and baiting.

There are quite a few different baits and sprays available for ant control at local hardware stores or pest control companies. There are also pest contractors available to do the work for you (look in the yellow pages).

The objective of bait is for the worker Ants (the ones you see running around) to take the bait back to the nest and feed (and therefore kill) the larvae and queens. If you don't destroy the queens, there will only be temporary reduction on the number of Ants until the queen is able to produce some more worker Ants and then the problem will be back. For invasive Ants one little portion of bait set out will not be enough. You will need to place out little portions of bait every metre covering a large space to ensure you are getting all of the colonies that may be there.

Ant Spray (or dust/sand) is used mainly as a barrier. Ants either don't like the spray or the spray will kill on contact. However, the larvae and queens won't be killed by the spray and the numbers will increase and cause problems again in a short period of time. Sprays can be used around houses or areas that you don't want the Ants to come into, however if there are Ants already in the area bait will help to get rid of them first. Sprays will need re-applying at constant intervals to maintain an effective barrier.

What Does Council Do?

Because the Darwin and Argentine Ants are widespread in Marlborough there has not been a specific programme instigated to control Ants. However, at Rārangi Beach, a small population of Argentine Ants are threatening a high ecological value site and therefore Council and Department of Conservation are collaborating to ensure the high ecological value is maintained by controlling Argentine Ants in that particular area.