[johan_M]

We have a small black ant that is a major pest in New Zealand and Australia.
It looks very similar to the Cape sugar ant that is native to South Africa.Lepisiota capensis. It is one of the few sugar ants that will drive out the Argentine ant that is also a pest over there.
Does anyone know if it is the cape sugar ant?

[SeanB]

Pictures?

Could be, they are common enough that they could have been taken in cargo to there.

[johan_M]

Sean,
  There is a "black house" ant listed as invasive but it's not the Cape sugar ant.
There is an African ant here.The  brown house ant(or pavement ant)  has just arrived and is focused only around the Auckland harbour area.
If you look at the distribution of all the ant pests, they have a strong focus around the biggest harbour which is Auckland. So to me this proves that,as you say, they have all arrived by container. The body that is supposed to control invasions is called MAF, but they aren't up to much. All they do is make you suffer at the airports with their  "bio control". They will confiscate any dried fruit or nuts but when it comes to preventing pests, they are hopeless.

 It is really amazing how the introduction of Pests over here has escalated. Over the last 10 years there is a huge list. Many agricultural industries are affected. Bee farmers, Kiwi fruit etc.