After eating the packet of chocolate buttons, Zachary, 21, turned his attention to the egg . . . but when he opened it up he found a live maggot in it.
His mother Isabel, 53, who lives at Kirkgunzeon, near Dalbeattie was mortified when he showed her the creepy crawly in the egg.
She had bought it at a Dumfries supermarket on March 4 as a surprise treat for her son.
Isabel said: “I was horrified when Zachary showed me what he had found.
“I just said ‘oh my God’. It was inside the egg and it was trying to eat its way out.
“You could see what looked like eggs on the side. It was horrible.”
Isabel has been disappointed by the response from Cadbury because after emailing them to tell them about her discovery there was no response and she had to telephone them on March 7.
“They said they would send me a package to send it back to them so they could investigate the whole thing.”
She added: “When I hadn’t heard anything I posted it on their Facebook page but it was the 19th before they sent packaging which was too small.
“The whole thing has been horrific.”
Responding to the claims, a spokesman for Mondelez, who own Cadbury, said: “At Mondelez, the quality of our products is of the utmost importance to us and we take all complaints extremely seriously. We are very sorry to hear about Ms MacDonald’s unpleasant experience and have launched a full and thorough investigation into this matter.
“We are in touch with Ms MacDonald and will update her on the results of our investigation.”