Tesco denies using deadly spiders

But the supermarket denied that food producers are using black widow spiders, after three customers found them in bags of grapes.

In separate incidents, the three women discovered the deadly spider among American-grown grapes bought from Tesco stores. Two of the spiders were alive.

The company says producers do use natural predators to protect fruit, as an alternative to chemicals.

But it strongly denies that the distinctive spider, whose venom is 15 times more potent than a rattlesnake, is deliberately used on suppliers' crops in the US.

Spokesman Jonathan Church said the use of natural predators, including harmless spiders, and less pesticides could have allowed the more lethal spiders into the fruit.

He said suppliers had been urged to step up checks on products before they are exported.

'It's dangerous'

"The idea is to reduce pesticide use by introducing natural predators instead, but we do not use black widow spiders.

"It is possible that is why the spiders in these three cases have got through because if we had used pesticides they would be dead."

Stephanie Thorneycroft, from Wimborne in Dorset, found a black widow, which has distinctive red markings on the underside of its abdomen, climbing up the side of a colander as she was rinsing grapes in her sink.

She told BBC Breakfast she disagreed with the use of natural predators.

She said: "I think it's dangerous because most children are eating the grapes before you get home.

'Quite rare'

"It can definitely kill - it can make an adult so poorly, and if you're bitten in this country, if you go to hospital, they're not going to know what's wrong with you."

Another woman living in Dorset and one in Merseyside also found the spider in their grapes.

Mr Church said although the cases were close together - all over the last few weeks - instances of this kind were "quite rare".

Tesco said it was looking into where the grapes came from and how the spiders had got into the fruit.