The Ministry for Primary Industries (MPI) says it is fielding calls from around the country from people who think they have found venomous Mexican spiders in their grapes.
The ministry is investigating after confirming 10 spiders were found in two consignments of table grapes imported from Mexico - some of them still alive.
MPI believes five of the spiders are black widows, while one is a brown widow and two are yellow sac spiders. All three of the species are venomous.
Further analysis is underway to confirm the identity of two other spiders.
MPI will review the rules for importing grapes, following the discovery of the spiders in the shipment from Mexico.
The ministry's manager of surveillance Brendan Gould said currently the fruit only undergoes visual checks.
"We have various measures from various countries depending on the risks and the goods themselves, in this case we've never had an issue with grapes from Mexico before ... but we've had this detection and we'll be relooking at our standards for grapes from there."
Mr Gould said that could mean more fumigations at the border.
He said it was first alerted on Friday night by someone in Wairoa, who found a black-widow when they went to eat their grapes. He said since then people from Auckland to Timaru had reported similar finds.
Mr Gould said people who had bought table grapes in the last few weeks should check they did not have any spiders in them.
He said none of the arachnids identified so far posed a risk to horticulture, and although they were venomous the spiders were not a serious threat to humans. MPI said they did not usually bite unless disturbed.
Supermarkets pull Mexican grapes from their shelves
Both major supermarket chains, Foodstuffs and Progressive Enterprises, have pulled table grapes imported from Mexico from their shelves.
Foodstuffs has confirmed a staff member found a live black-widow spider at Rolleston New World on Monday, and its customers have also found some.
The company said MPI's clearance process for allowing products like grapes into the country usually involved only a visual inspection, and fumigation was not routinely required.
Foodstuffs said since the discovery, it had asked all importers of Mexican products to prove their product has been fumigated.
Progressive Enterprises, which owns Countdown supermarkets, has also responded, withdrawing Mexican grapes from its South Island stores. It said its North Island stores did not receive any of the grapes from either affected consignment.