A tourist is lucky to be alive after a deadly spider bit him on the penis.

The Canadian backpacker was attacked after skinny-dipping in New Zealand.

While he was swimming, a rare katipo spider crawled into the shorts he had left on the beach. When the man returned, he put them back on and fell asleep — but the trapped spider then nipped him on his manhood.

Within minutes, the spider's venom was causing him to have agonizing chest pains, a racing heart, high blood pressure and severe swelling to his penis.

Dr. Nigel Harrison, who treated the 22-year-old at Dargaville Hospital, revealed the case in a report for the New Zealand Medical Journal.

"It was a rather nasty, ill-placed bite,” Harrison said. “The man woke to find his penis swollen and painful with a red mark on the shaft suggestive of a bite. He rapidly developed generalized muscle pains, fever, headache, photophobia (light sensitivity) and vomiting."

The unidentified man's condition "improved rapidly" after treatment with an anti-venom, but he was kept in the hospital for 16 days before being allowed to return to Canada.

The katipo, a Maori word meaning "night-stinger,” is an endangered species in New Zealand.

The pea-sized spiders are related to the American Black Widow. Bites to humans are rare, but two fatalities were recorded in the 1800s.