A mother was horrified when she opened a bag of Tesco bananas and discovered something deadly lurking inside.

The fruit was infested with eggs of the Brazilian Wandering Spider, the world’s most venomous spider, which can kill a human in under an hour.

Maria Layton, 43, said the eggs started to hatch after she opened the bag for her daughter Siri, six, so she immediately put the whole lot into a sealed container.

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Cocoon: The Tesco bananas were infested with dozens of deadly Brazilian spiders hatching from eggs

‘I’m glad it was me rather than Siri that opened the bag,’ she said yesterday.

The bite of the Brazilian Wandering Spider can also give a man a painful four-hour erection – its venom is currently being studied for use in erectile dysfunction treatments.

The bananas, shipped from Costa Rica, had been bought at a Tesco store in Pontardawe, South Wales, by Mrs Layton’s husband and taken to their home in Bristol.

Mrs Layton said: ‘Siri asked for a banana. The first banana had a funny bit on it, so I got another one for her and that was when I found the massive spider cocoon.

‘I remembered seeing a news story about them, so I Googled it. I went through the images and there was an image which looked very similar to mine.

The spiders' nest may have been exported with the bananas, which were shipped to the supermarket from Costa Rica

‘I was so scared – I don’t like spiders at the best of times, but have read about the Brazilian Wandering Spiders and was very frightened about the potential threat.

‘The spider cocoon started to unfurl so I put it in a sealed box and put it in the freezer as I read that is supposed to kill them.’

Shocked by the possible danger to Siri and her three-year-old sister, Phoebe, Mrs Layton contacted Tesco customer services, which told her to take the bananas, deadly spiders and all, back to the store – so that the barcode could be scanned and the store could refund her money.

She said: ‘Tesco were a bit useless. I really wanted some helpful advice on how to act.

‘Tesco failed to see the potential threat to me and my family and thought I was only interested in having a pound or so back. I called Food Standards but they said it wasn’t anything to do with them, I called Trading Standards but they were shut.

‘I spent an hour and a half ringing round trying to get some help while I had this potentially killer spider in the house.’

A Tesco spokesman said: ‘Our policy is for the customer to take the product to the store where it can be investigated. We don’t have a service whereby someone can go out to the home.

‘We’ve apologised to Mrs Layton and offered a gesture of goodwill. We’ve asked her to return the product to our store so we can conduct a full investigation.’

It is not the first time the venomous spiders have been found in people's fruit bowls.

Last October a family found a lethal Brazilian Wandering Spider among their Waitrose bananas.

A Waitrose worker came round to catch the spider, but by then it had escaped, meaning the supermarket had to send in a pest control expert.

Meanwhile a mother-of-one from Colchester, Essex, had to incinerate her vacuum cleaner in September after a cocoon on one of her Tesco bananas burst, sending eggs flying on to the floor.

Abby Woodgate, 30, was told by pest control workers that anything that came into contact with the eggs would have to be burned to ensure there was no chance of the baby spiders surviving.