Tesco said it was "horrified" to hear that customers found maggots crawling in a box in the confectionery aisle of one of its stores.
Josh Downs and friend Braden Little, both 18, made the grim discovery in a box of Cadbury's Caramel Nibbles in the Tesco in Roker Avenue, Sunderland.
They claimed people walked out of the supermarket in disgust and the pair later put a photo of the maggots in the box on Twitter.
Mr Downs told the Sunderland Echo newspaper: "I didn't realise what it was at first - I thought it was caramel leaking out of the packet.
"I felt something move and saw the maggots on my hand and my clothes. It was disgusting."
The retail giant said it was investigating the incident in what was a busy aisle that would be frequently re-stocked and cleaned.
A Tesco spokesperson said: "We were horrified to hear about this and are grateful to the customers who brought it to our attention.
"This area of the store is regularly cleaned and filled with new products. We are conducting a full investigation."
Seven of the craziest supermarket glitches
Maggots found in supermarket aisle
One of the most popular glitches, was a wine deal at Tesco back in November 2012, where a series of offers clashed, leaving a bottle of £9.99 wine selling for £1.50.
The 'three wines for £10' deal apparently clashed with a '25% off when you buy six or more bottles' deal. The 25% was accidentally taken off the original price rather than the reduced one, leaving the wine at rock bottom prices. Deal-hunters cleared the shelves around the country.
Perhaps the most popular glitch from Tesco came in June 2011, when instead of taking £4 off the cost of a £20 case of beer, the supermarket accidentally started selling the cases for £4. The ensuring rush was nicknamed the 'beer stampede'.
Sadly not every supermarket pricing glitch comes with such a happy ending for consumers. In March last year the bargain-hunters thought their luck was in, when Tesco accidentally priced the new iPad at just £44.99 instead of around £650. Sadly it spotted the mistake before shipping the goods. The small print on its website meant it could refuse to sell at this price, and refund their customers instead.
In September 2012, Asda was responsible for one of the most expensive glitches. The Asda Price Guarantee offered vouchers to customers who could have got their shopping cheaper elsewhere.
However, when certain trigger products were in the basket, the supermarket massively under-priced the shopping at other supermarkets, and offered huge vouchers to shoppers. In many instances the vouchers came to roughly the same as the cost of the shopping.
In April, a mistake on their website resulted in Tesco selling 8 packs of Bulmers cider 568ml bottles for £5 - rather than a six pack for £8.
Deal-hunters snapped up the deal online, and had varying degrees of success. Some had their order delivered in full, others had six delivered for £5 - and were able to negotiate their way to another two, while others were offered six for £5 or their money back.
October last year saw one of the most famous glitches, when Tesco Terry's Chocolate Oranges were subject to two deals at the same time, and the price dropped from £2.75 to 29p. There were plenty of people getting chocolate oranges last Christmas.
A buy-one-get-one-free deal went awry at Tesco in March. People putting four tubs of I can't Believe It's Not Butter or Oykos yogurt packs into the trolley were only being charged for one.
Soon the online deal-hunting community was in action, with one person bagging 50 tubs of butter and 22 pots of yogurt for £8.79 - a saving of £133.89.