A spider inadvertently found in a packet of grapes by a West Auckland woman has been confirmed as an Australian redback.

The spider was found, alive, earlier this month by West Harbour resident Debbie Bellingham after she bought a bag of red Australian grapes from her local Countdown supermarket.

"My daughter came down to me and goes, 'Mummy, there's a funny looking spider in the grapes, it's black and sort of orangey-red'," she said.

After consulting a biosecurity hotline Ms Bellingham was told to freeze the spider and post it to the Ministry for Primary Industries (MPI).

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Mrs Bellingham said she was worried about her 3-year-old daughter who had been eating the grapes.

Redback spiders are native to Australia and have a venom toxic to humans with bites causing severe pain. Established populations exist in central Otago and Taranaki.

A MPI spokeswoman said the ministry concluded its investigation into the find this week and confirmed the spider was a redback, Latrodectus hasselti.

"All biosecurity risk associated with this detection was mitigated with the killing of the spider," she said.

No changes to the Import Health Standard for grapes from Australia had been planned as a result of the find.

"MPI will monitor any trends in post border detections of redbacks."

Following the confirmation, Ms Bellingham said she was concerned that her find was followed by the discovery of a Queensland fruit fly this week.

"If a redback can get in alive, what else is getting in," she said.

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A Countdown spokeswoman said an internal audit tracing the batch of grapes had been completed.

"We can confirm that the shipment it came from was treated appropriately then inspected and cleared by MPI in New Zealand before we received it.

"We've had no further issues reported to us since."

MPI said grapes imported from Australia were fumigated with sulphur dioxide and carbon dioxide and a proportion were visually inspected.

"Very occasionally things do get through despite treatment and inspection," a spokeswoman said.

The ministry had confirmed two other redback sightings in the past six months, a single specimen in the garden of a Rotorua resident in late January and another in an empty shipping container from Australia in Wellington last November. Both were found alive.

An Auckland District Health Board spokeswoman confirmed they had stocks of anti-venom on hand.

If people believe they have found redbacks, they can call MPI's pests and diseases hotline on (0800) 80 99 66.