Karl Gaskell and his wife Nicki, from Castletown on the Isle of Man, purchased the natural holiday decoration, made from branches and straw, from a Co-op supermarket.
However, shortly after hanging the wreath, the couple and their two daughters noticed a strange smell emanating from the decor and upon closer inspection, saw grey scaly bulges poking out from the frame of the decoration.
At that point, Gaskell cut open the straw holding the wreath to find a dead grass snake.
It is thought that the snake crawled into the straw to hibernate before the stalks were collected and squashed up to make into the £12 decoration.
“I don't know what compelled me to put my nose up to the wreath after I spotted these strange grey scales, but I did,” Gaskell recalled. “You could tell it was some kind of dead animal - a reptile, not a mammal.”
According to the father-of-two, his first concern was the possibility that the snake was poisonous, as “poisonous snakes remain poisonous long after they've died” - so he sought help from the Natural History Museum.
Fortunately, the dead snake was identified as a non-venomous Natrix natrix, or grass snake, according to the museum, which informed the family that these snakes hibernate in straw piles.
"They do hibernate in straw piles and I see fresh cereal straw in your photo,” the email from the museum said. “You may find sources calling the British grass snakes Natrix helvetica, after a recent split (2017).
In response to the incident, the supermarket told Gaskell it would be talking to its supplier to “find out how this has happened”.
“I can only imagine how upset you must have felt and I really am sorry,” a spokesperson said. "We want our products to be the best they can be and for you to find what you did is not good enough. We will refer this to our suppliers and also make our technical team aware.”
In a separate statement, the company expressed its shock and said “this is not something we have previously experienced”.
Since the incident, the family has vowed never to get another Christmas wreath.
"We were just super unlucky I think, because it was the first wreath we'd bought ever,” Gaskell said.