Ant nests, Fire ants, Ants; where there is one there are many. NZ has 40 different species! To get rid of ants the following measures are a good place to start -
Cover all left overs, using air tight containers and store in a hard to reach place
Regularly wipe down food preparation surfaces using a disinfectant cleaner
Find the Colony and destroy the source of the problem.
An individual ant can live up to a year. Once they have located a good food and moisture source a colony could be in for the long haul and if left unattended could grow to a large scale. Read More about Getting Rid of Ants.