Abbi Rigby purchased a bunch of grapes to give to her children from her local Asda on Tuesday afternoon.
But the 31-year-old claims to have found a poisonous African spider crawling around among the fruit.
The mum-of-three has said she was horrified when she was saw a spider’s web and a black, eight-legged creature wriggling around inside the cellophane wrapper.
Shockingly, she had already opened the £1.45 packet earlier in the day and had eaten some of the grapes at work before going to pick up her three daughters from school.
She took the creepy-crawly home and researched it online to discover it was a venomous African Sac spider, commonly found in South Africa.
Rigby contacted the supermarket giant to complain and was told the creature had travelled over 2,000 miles to Britain from Morocco.
On Thursday, Rigby, who is an office manager from Newcastle-under-Lyme, Staffs, said: "The worst thing is that I did actually check the box before I ate any of the grapes.
"I had grapes at work before I went to pick the kids up from school and only noticed the spider when I was parked up waiting for them.
"I saw something white and furry and it was a web. I looked inside the web and there was this spider. It was small but I panicked. I'm petrified of spiders. What if I had picked up the grape it was on and eaten it?
"At first I thought it was dead but I saw a leg moving. Then it moved quicker and quicker.
"It had got a black face and I soon recognised it was an African Sac spider. I know these are from Africa so I rang Asda to find out the country of origin and they said it was Morocco."
She added: "I've done a lot of research and can't see anything else with the distinctive black markings on its face. Asda have said it definitely looks like an African Sac spider. I managed to take a few pictures, but I was not going to touch it.
"I thought it was dead when I first saw it in my car, but then it was moving a lot so I took some footage of it – and it was definitely alive.
"Luckily I spotted it before my children got in the car, otherwise it could have bitten them. I have heard so many stories about these sort of things. It has put me off grapes forever now."
The supermarket told Rigby they are investigating the incident and admitted they may have to recall the product.
A spokesperson for Asda said: "We'd like to reassure Mrs Rigby and our customer's that checks are taken place on our fruit, however sometimes insects tag along to give us a fright.
"We're currently investigating and will be in touch with Mrs Rigby soon."
A spokesman from Staffordshire Wildlife Trust said: "It is relatively uncommon these days for a spider to arrive in Britain in conditions like this.
"With modern refrigeration, spiders and other invertebrates don't usually survive."
The African Sac spider accounts for more than 70% of bites in South Africa.
Their venom causes the death of tissue around the bite, and symptoms normally become appear between two and eight hours afterwards.
The creature’s venom can remain for 24 hours after a bite. Bites typically appear as two tiny yellow-green spots around 4-8mm apart – where the fangs have penetrated.