Ceri and Rose Williams suffered numbness, head aches and high blood pressure after eating the fruit they purchased in Tesco.
Mr Williams, 52, and his 45-year-old wife had already started munching on the two £1 bags of fruit when they noticed that something was moving inside.
A quick rummage revealed that two spiders, one alive and one dead, had already made a meal out of the Moroccan-grown grapes.
Mr Williams also spotted a cotton wool-like substance - which turned out to be the poisonous arachnid's nest.
Minutes later, Mr and Mrs Williams, who were on holiday in Newquay, Cornwall, fell ill and drove to hospital where doctors told them the fruit they had eaten had been covered in the spider's toxins.
They were monitored closely for several hours and have now made an official complaint to the supermarket in Wadebridge, Cornwall - which has offered to pay them back the £2 cost of the grapes.
Environmental health officers identified the beasts as false widow spiders - Latin name Steatoda nobilis - cousin of the famous Black Widow.
A spokesman for Tesco, said: 'With all the expertise, checks and will in the world it is not always possible to completely legislate for the natural world. It must have been a real scare.'
But Rose added: ''They've offered a £2 refund, which is a bit cheeky considering we were half scared to death.'
source: http://www.mailonsunday.co.uk/news/article-1035633/Couple-poisoned-eating-cut-price-supermarket-grapes-tainted-spider-venom.html