UK supermarket retailer Tesco has denied it has been using black widow spiders as a form of pest control after three customers found the deadly spiders in bags of grapes within the last few weeks.

In one incident, Stephanie Thorneycroft of Wimbourne in Dorset spotted a black widow spider in her colander as she washed the Tesco American-grown grapes. Two similar incidents occurred – one in Merseyside and another also in Dorset.

Black widow spiders have distinctive red markings and venom that is fifteen times more potent than that of a rattlesnake, reported BBC Online.

Tesco spokesman Jonathan Church said reduced pesticide use was to blame for the incidents. Producers sometimes use natural predators such as spiders to kill insects rather than using chemical pesticides, but Church denied that black widow spiders would have been used. He admitted that it was possible that the spiders survived because no chemical pesticides had been used on the grapes.

Church said suppliers had been urged to increase checks on products before they are exported to the UK.