Isolde Beesley, complained that the creature fell out as she poured a glass of Moscatel de Valencia, a white Spanish dessert wine, at a family celebration.
She claims has suffered stomach pains since drinking some of the wine, having initially failed to see the thumb nail-sized amphibian floating at the bottom of the bottle.
Miss Beesley, from Liecestershire, said she had bought the £3.58 bottle on December 23 last year and opened it on Boxing Day.
She told Decanter magazine that she had since passed the bottle on to her local trading standards office and complained to the company prompting it to temporarily take the wine off the shelves.
She has also hired a solicitor and is attempting to bring legal action against the company accusing it of selling produce which is unfit for human consumption.
A spokeswoman for Asda said investigations had found no problems with the bottling process or pests present at the factory.
“We are at a total loss as to how this could have happened,” a spokeswoman said.
“It’s nigh on impossible for any object to find its way into a bottle of wine when it is being produced.
“It simply can’t happen. So somewhere along the line between it being bottled in Spain, opened and being drunk, our unwanted guest has found its way into her glass.”