The tourist fell asleep naked on a beach in Northland, on the far tip of the north island, after going skinny dipping, the NZ Herald reported.
After the bite from the highly poisonous katipo spider, the 22-year-old began to suffer high blood pressure, rapid heartbeat and a severely swollen penis.
Whangarei Hospital's Dr Nigel Harrison wrote in the NZ Medical Journal that the tourist realised he had been bitten as soon as he woke up.
"He rapidly developed generalised muscle pains, fever, headache, photophobia [light sensitivity] and vomiting," he said.
"It was a rather nasty, ill-placed bite."
After being treated at Whangarei and Auckland Hospitals over 16 days, the tourist was discharged and returned to Canada.
The venom of the katipo spider (pictured), which is related to the Australian redback, was previously not known to cause heart problems in humans.
