A British man on Wednesday admitted delivering a package containing a venomous tarantula to a work colleague the day he handed in his resignation.

At Leicester Magistrates' Court in central England, Mahlon Hector, 22, pleaded guilty to delivering a rare Mexican red-kneed tarantula in a box addressed to a woman colleague at the branch of the store Marks & Spencer in Leicester, where they both worked. At the same time, he handed store bosses his resignation.

The intended recipient, Susan Griffin, was not hurt.

Hector is to be sentenced later on the charge of sending a letter or other article conveying a threat on March 28. He did not reveal his motives in court Wednesday.

When staff at the store discovered the spider they alerted the Royal Society for the Prevention of Cruelty to Animals, which took it away.

"It was a daft [stupid] idea. They are not the most dangerous spider, but it could be fatal if it is given to someone who has an allergic reaction to it," the society's spokesman said Wednesday.

"The woman who received it must have been terrified."

The Mexican red-kneed tarantula — Latin name Brachypelma Smithi — is commonly used in movies because of its scary appearance.

With a leg span measuring up to 10 inches, it has a hairy dark brown body and reddish-orange leg joints. Each leg ends with two claws which are used for climbing trees.

It is said to bite rarely, but flicks its hairs at victims.

It is the only tarantula listed as rare by the Convention on Trade in Endangered Species.