The creature was dead when staff at Sheffield's Botanical Gardens discovered it in a pavilion but it is a mystery how it arrived in Yorkshire.

The species earned its name as a result of its distinctive skull-like markings on its back and is the largest moth to be found in Britain, with a wingspan of up to 13 centimetres.

It is most commonly found in southern Europe; generally only a few are recorded in this country and those almost exclusively in the South.

Gardeners discovered the dead specimen in Sheffield and took it to moth enthusiast Ed Kelly, who runs the Gatehouse gift shop at the gardens.

He identified it and also called in a moth expert from Sheffield University.

A spokeswoman at the shop said: "The moth is currently on our mantle piece but it will be given to Sheffield University or one of the museums in the next few days.

"It has created a lot of interest from customers. It had not fully opened its wings and seems to have died before it was fully developed, it seems to have just come out of its chrysalis."

One theory was that it could have been transported to the gardens in a delivery of soil, but none had been acquired recently.