Dad Jamie Roberts, 31, spotted white patches in the fruit after putting them in a bowl, but assumed the marks were simply mould.
However, closer inspection revealed a spider nest containing hundreds of the eight-legged creatures.
Jamie - who already suffered from arachnophobia - and his wife Crystal called pest controllers, who warned them to leave their home immediately.
While the spiders have not been officially identified, the family believe they may be the Brazilian Wandering Spider.
According to the Guinness World Records, the species is the world's most poisonous spider, with venom said to be 30 times more powerful than that of a rattlesnake.
It was like something out of a horror film because suddenly the window sill was moving with hundreds of these spiders.
My wife and I rang the shop where we bought them and they asked us to drop them round to them.
When we did they called pest control and they told us to get out of the house.
They said they couldn’t be sure what kind of species of spider they were because you can only do that when they are fully grown but they looked identical to the deadly Brazilian Wandering Spider.
“I unpacked the bananas from the cellophane wrapper and put it in the bin so it’s possible the ‘queen spider’ may have been in there," she said.