People in parts of Whanganui are being pestered by ants biting them in bed at night or swarming up their legs while they hang out the washing.
City pest management technician Gary Clark has been getting up to six phone calls a day, asking for help to control them. He says help is at hand with a new product.
The ants are an Argentine species relatively new to the area.
They seem to be established in three parts of the city, Mr Clark said. Those are St John's Hill, Gonville-Castlecliff and the central city, especially Campbell and Bell streets. A fourth part may be on the way - he's been getting a few calls from Aramoho lately.
In warm weather the ants are "rampaging", he said. They boil up out of the ground and up the arms of people who are gardening, and they walk shoulder to shoulder in wide groups along fencelines and mowing strips.
In winter they go into a form of hibernation. There is less activity, but still a few ants out foraging.
Mr Clark went to a whole day training seminar in Wellington on Wednesday, run by pest control product retailer Garrards. He was told about a new product that is more effective than usual ant control poisons. Some ant poisons work quickly. Foraging ants that try them return to their colony sick. But Argentine ant colonies have guards and the guards don't let sick ants inside.
The new product is slow-acting. It takes the ant who first eats it three days to die, so she takes it back into the colony and spreads the poison to others, killing more in a cascade effect. The product also has very low toxicity to mammals - including people, cats and dogs.
Winter is a good time to take action against Argentine ants, Mr Clark said, even though they may be out of sight and out of mind.
In winter there are fewer ants out foraging and it's more likely that all of those foragers will find the poison and take it back to the nest, killing others.