Up to six redback spiders a year are found in cargo at Port of Napier and other insects and pests are also common, says a Ministry of Agriculture and Forestry (MAF) spokeswoman.
MAF staff at the Port of Napier found redback spiders every two or three months and other invaders included ants, crazy ants and black widow spiders - the latter particularly in consignments from the United States. When these pests and insects are found the consignment is fumigated.
Research released this month shows that while redback spiders prefer warm, dry areas, they like urban areas more than their New Zealand cousin, the katipo. The spiders are already settled in Central Otago, and Hawke's Bay's warm climate is ideal for a colony, said the research.
Te Papa entomologist Phil Sirvid said for a redback population to develop in a new area more than one spider would need to come in through imports. But a female with egg sacks might be enough to start a breeding population.
"At the end of the day it comes down to getting enough in one place to form a breeding population and we're lucky it hasn't happened," he said. "It can happen and it could happen again."
The proximity to the beach could be a concern because it was an opportunity for the immigrant redback and the native katipo to meet and potentially crossbreed.
Katipo were recently declared an endangered species and DNA analysis showed Katipo had bred with redback spiders before.
"Our concern is we could lose a rare and protected species due to hybridisation," Mr Sirvid said.
If redback spiders did settle in urban Hawke's Bay, locals would likely only find them by accident, in sheltered areas near the ground.
Redbacks would only bite if someone put their hand on a spider. Bites were very painful but the amount of venom released depended on how recently the spider had hunted and severe bites were treatable with anti-venom.