Brazilian wandering spiders - among the most venomous in the world - were discovered when a family was unpacking shopping from an unnamed ASDA.
The family noticed a small, white cocoon on the side of bananas they had purchased from the supermarket giant and dropped them in panic, according to reports.
According to wildlife experts the spider, also known as the Banana spider or Armed spider, can cause long and painful erections in males, followed by death, within a matter of hours if bitten.
A potent neurotoxin in the venom can also cause abdominal cramps, hypothermia, blurred vision and convulsions.
While the poisonous arachnids are found throughout South America, particularly in Brazil, they have also been known to hitch a ride to North America and Europe among bunches of bananas.
According to reports ASDA has since apologised to the family and promised a full investigation.