New research shows redback spiders are living in New Zealand in greater numbers and could be breeding in new areas.
They have lived in New Zealand for decades but now the Ministry of Agriculture and Forestry (MAF) fears the deadly spiders are increasing their numbers in populated areas.
Dr Doug Lush from MAF biosecurity said the spiders could pose a problem to human health, and that customs officers are vigilant in trying to stop the spiders arriving. But he said it is difficult to get every single one.
Colonies are likely to be found in urban Auckland, Tauranga, Gisborne, Hawke's Bay and central Otago.
The spiders tend to live in rocky outcrops, vineyards, grasslands and dry areas under houses.
Agresearch said the spiders are causing problems in central Otago where they could be feeding on endangered beetles and skinks.
The spiders arrive in New Zealand on shipping containers crossing the Tasman.
The good news is that no one has been killed by a redback in more than 50 years in Australia since anti-venom has been available.
MAF is urging people to get in contact if they see a redback spider.