When you arrive to your new place and find a package marked 'return to sender,' you might not want to open it - there might be a giant, hairy spider inside!

That's what happened to a U.K. man - a package marked 'return to sender' sent to his new address contained a Brazilian Salmon Pink Birdeater, the third largest spider in the world.

The package had remained unopened for 3 weeks and the bedding inside had gone moldy. The tarantula was alive, but not well.

The man took the spider to Highcroft Veterinary Group in Whitchurch, where it was determined to be dehydrated and had lost a lot of hairs from its abdomen.

The Brazilian Salmon Pink Birdeater can grow to have a leg span of 28 centimeters and are known to be semi-aggressive. It has 2.5 centimeter-long fangs and is capable of "kicking" hairs from their abdomen in self defense - which can be a skin irritant and cause blindness.

"Mould can affect tarantulas very negatively so, with the exposure to the fungus and being stressed after circulating in the post for so long, I'm surprised it even survived," said Sonya Miles, a veterinary surgeon at Highcroft. "It is common to send insects and some living creatures via the post, as long as they are clearly labelled in accordance with the postal service being used."

Miles took in the spider, who she calls Sid, to recover at her rescue center. She hopes to find Sid a new home once he calms down and can be handled.

If you're looking to own a pet tarantula, check out these helpful tips from Petsmart.