A black widow spider. Five have been found in shipments of grapes from Mexico.

The bite of the spiders found in imported grapes causes a pain "like having your skin ripped off".

Supermarket chains are pulling Mexican grapes from their shelves after the discovery of 10 venomous spiders since Friday.

The Ministry for Primary Industries (MPI) confirmed it has received 10 reports of spiders found in grapes at several locations around the country - five black widows, one brown widow, two yellow sac spiders and a further two have yet to be identified.

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The Ministry has been working with New Zealand produce retailers to have all imported Mexican grapes withdrawn from sale.

MPI manager of surveillance Brendan Gould said it was likely some grapes from the affected shipments will have already been sold and the Ministry is advising people who have bought imported grapes in the past few weeks to be on the lookout.

"We recommend that if people have recently bought imported table grapes, they should carefully check them for the presence of any insects. In the unlikely event that they find a spider, they should immediately bag the grapes (and spider/s) and seal them, and contact our Hotline 0800 80 99 66," Gould said.

He said there are strict controls in place for the importation of grapes from other countries.

In the case of Mexico, grapes are inspected visually and fumigation is only done if spiders and other pests are identified.

"We take this matter very seriously and we are investigating how this breach has occurred and taking measures to tighten up the system," Gould said.

He said importers of Mexican grapes in transit here are being given the option of treating or destroying them on arrival in New Zealand.

Mexico's exporting season for grapes has now finished for the year, he said.

The Ministry said none of the spiders identified to date pose a risk to New Zealand's horticultural industries.

Foodstuffs corporate PR director Antoinette Laird confirmed one spider was discovered in grapes at New World Rolleston and other Foodstuffs stores have reported similar finds.

She said Foodstuffs has been working with MPI on the issue.

"Foodstuffs has taken a very conservative approach to withdraw all affected product as customer safety is our top priority," she said.

Foodstuffs was alerted on Friday to the potential discovery of black widow spiders in Mexican Desert Pride Red and Black grapes, which has since been confirmed.

In a statement, Foodstuffs said product from the suspected batch was withdrawn from sale on Friday and on Monday, all Foodstuffs stores in both the North and South Islands have withdrawn all Mexican green, red and black grapes from the shelf.

Additional steps have been required for all importers of grapes from Mexico to show evidence of product fumigation before accepting them into stores for sale.

Foodstuff said its customers should inspect and wash all grapes before consuming them.

A Countdown spokesperson said MPI requested Countdown, owned by Progressive Enterprises, withdraw all grapes from Mexico from sale. They had been distributed to Countdown stores in the South Island.

Countdown immediately complied with the withdrawal and removed Mexican grapes from sale from North Island stores on Wednesday.

The spokesperson said no spiders had been sighted as yet and they would implement more extensive inspections of the grapes.

MPI also requested additional fumigation.

One of the spider discoveries was made in Wairoa by a teacher at education and childcare centre Kids' House.

The teacher, Aira Bremner, told The Wairoa Star she was washing a bag of Mexican red seedless grapes when she noticed a black spider tumble out and fall onto the chopping board.

The spider was identified by MPI as a black widow.

A similar case of black widows being found in grapes, which also came from Mexico, happened just one month ago in Warwickshire, England.

The man who found the spiders in a bag of purchased grapes found a number of baby spiders crawling around the grapes.

Upon further inspection by a local wildlife sanctuary, there was found to be an entire nest inside where a spider had given birth.

SEARING PAIN

Curator at Canterbury Museum and spider expert Cor Vink said the chances of dying from a bite from any of the discovered species of spiders were very slim.

"What widow venom does is it causes an extreme amount of pain and that doesn't respond to usual pain medication. But anti-venom is easily available," he said.

Vink said the pain had been likened by people to having their skin torn off.

Widow bites cause a lot of sweating, with pain starting roughly half an hour after the bite. There may also be nausea and breathing problems.

Yellow sac spiders also have a painful bite but far less so than widows and they do not cause any serious health threats. Anti-venom was also available for bites from this species.

Vink said the chances of getting bitten by these types of spiders was also low because they prefer to hide away, which was probably why they managed to get onto the shipment of grapes.

"They really stay out of people's way. You'd have to pick them up and handle them or get them caught in clothing," he said.

Vink recommended anyone who gets bitten by a spider to catch it, get it identified by a spider expert and seek treatment from a doctor.

New Zealand already has its own species of widow spider found on beaches ranging from the north of Dunedin to the top of the North Island.

But those numbers were thought to be declining due to increased construction of houses and vegetation taking over beaches.

Vink said there were only two reported deaths from this species, both of which were children in the 1850s who died of complications.

Central Otago is also home to the Australian redback spider, which Vink said was threatening the existence of the Cromwell Chafer beetle, a rare species found only in New Zealand.

If other species of spiders managed to establish themselves in the country, there could be dire consequences for New Zealand's native fauna.

"Any spider that establishes here can potentially have effect on native fauna because spiders are all predators. They can also displace other spiders.

"In New Zealand we have an estimated 2000 species of spiders and 90 per cent are found nowhere else in the world. There's even more insects in New Zealand and about 95 per cent of them are only found in NZ as well.

"Any threat to them is pretty serious."

Anyone bitten by a spider should contact their doctor. Information is also available by calling the Ministry of Health's Healthline on 0800 611 116.