This is an Argentine Ant. You can find heaps of information about their invasion of parts of New Zealand on the internet. For example, in Te Ara, The Encyclopaedia of New Zealand, we read:
Argentine ants (Linepithema humile) are one of around 28 introduced ant species in New Zealand. They are very aggressive and can eliminate other ant colonies, and also destroy and eat other insect species and earthworms. These invasive species pose a great threat to many forest floor invertebrates that have evolved in a land without aggressive ant species. Although they breed prolifically, Argentine ants do not fly but walk to establish new nests. This means that they do not spread rapidly, but an infested site has a very high number of ants and colonies which merge into one vast super-colony that extends over a very large area. Their natural rate of invasion is a few hundred metres per year.
We have a bach at Mangawhai. Had it for a few years. About two years ago I began to notice there were different coloured ants about. We had already dealt to the usual NZ black ants (using the liquid they collect and take back to their nests), but these little reddy-brown buggers were different. For a start they can bite. As you can see on this picture, Argentine Ants are surprisingly small. But they can deliver a sharp bite.
When I was an ARC Councillor (2004-2010) we periodically received advice about Argentine Ant infestations. I recall the main infestation of concern was on Great Barrier Island, in the Gooseberry Bay area. At the time it didn't occur to me that there were infestations on the mainland.
I contacted ARC and Northland Regional Council after doing a bit of research, because I found that it was possible to obtain Argentine Ant control chemicals for free. Apparently a deal had been done with Department of Conservation, which was concerned about the spread of this pest into forests.
I was informed that free Xtinguish (the recognised control) was no longer available free. You can get it on TradeMe from Ant Busters. But it costs $40 for 100gm in a sort of syringe like applicator.
Rather than buy Xtinguish I experimented a bit with fly spray and generally made myself unpopular with the local ant population. However I soon learned they could set up nests anywhere and everywhere, and no sooner had I dealt to one nest, then it would somehow develop into several nests. I found out about multiple queens and all that stuff. Argentine Ants form nests in the lawn, in gardens, in trees, under the door mat, at the top of verandah posts, and anywhere inside a building.
Listening to the marine radio a few months ago - the one that gives the tides and wind speeds and marine forecasts - I was intrigued to hear a message to boaties to make sure there were no Argentine Ants on board their boats before they headed out, potentially to stop for a picnic or for a spot of diving, at one of the many islands in the Hauraki Gulf. I was well aware from my own experience how it only takes a blade of grass, or a drooping branch, and a few hours, before you have a resident group of Argentine Ants on board your boat on its trailer.
This Christmas a mate came to visit from Devonport, Auckland, brought his boat up, and was surprised to find it crawling with ants the next day. He was only aware of the risk because we'd been talking about it the night before. These ants are tiny - about half the size of your typical NZ black ant - and innocuous looking. You have to be very aware of them to notice them at all.
They are also spectacularly invasive, organised, and voracious.
I've no doubt there are significant infestations in parts of urban Auckland now. These will grow unless checked, and become a more serious problem for Aucklanders and the environment.
In January I finally purchased a 100gm tube of Xtinguish. The advice is to lay blobs about the size of what you put on a toothbrush, outside every two metres square or so. I have to say it has been very effective. So far. For our property. But I am aware that neighbours are also infested. The risk of widespread infestation of Auckland from Mangawhai must be high. Should this invasion worry us?