Supermarket chains are pulling Mexican grapes from their shelves after the discovery of 10 venomous spiders.
The New Zealand Ministry for Primary Industries (MPI) was investigating and said it believed five of the spiders were black widows, one a brown widow and two were yellow sac spiders. All of those species were venomous.
It was looking into the identity of the two other spiders.
MPI said they could be dangerous to people who come into contact with them but did not pose a threat to the horticultural industry.
Foodstuffs supermarket said in a statement it 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.
Product from the suspected batch was withdrawn from sale on Friday and on Monday, all Foodstuffs stores in both the north and south islands have withdrawn all Mexican green, red and black grapes from the shelf.
The company said it had taken additional steps requiring all importers of grapes from Mexico to show evidence of product fumigation before accepting them into stores for sale.
It advises customers to visually inspect and wash all grapes before consuming the product.
It said product withdrawals do happen from time to time and stores were following the normal processes associated with this.
Radio New Zealand reported Progressive Enterprises, which owns Countdown supermarkets, had also withdrawn Mexican grapes from its South Island stores but not from its North Island stores as they did not receive any of the grapes from either affected consignment.
No details were given as to where in New Zealand the spiders were discovered.
MPI, Foodstuffs and Progressive Enterprises have been contacted for comment.
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 antivenom 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. Antivenom 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.”
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