Eric Crossley plunged into the calm ocean off Broome, Western Australia when he felt a sting on his neck.
The waters are an emerging "hotspot" for a "mysterious", highly-venomous animal that's near invisible to the naked eye.
The British national and professional diver was working for Clipper Pearls when a tiny, and potentially deadly, Irukandji jellyfish slipped past his loose diving hood on March 2018, about six kilometres off Quondong Beach.
Crossley told 9news.com.au for the next 10 hours his body would be locked in an excruciating battle against pain.
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The then 30-year-old made his way back to the boat to sit in the galley as the crew mobilised around him.
'The first 10-20 minutes it's kind of nothing, but it becomes very apparent quite quickly something significant is happening," Crossley said, explaining the pain comes in "waves"'
"It feels like someone has turned on a switch which has activated every single nerve in your entire body, like you're on fire without being on fire.
"I got hot and cold waves, started puking. You feel nerve sensations in parts of your body you haven't.
"The closest thing I could probably compare it too would be incredibly severe food poisoning. Your body is twisting and cramping and clamping in order to push out whatever toxin it is.
"My body was just tensing up, it has no idea what to do."
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As Crossley was stung in a remote location, it took about three hours for him to reach a hospital.
The last hour included a "horrible and bumpy" four-wheel-drive.
When he finally did make it, another challenge emerged – finding painkillers strong enough to take the edge off the agonising sting.
"They gave me 150 mcg of fentanyl and an hour-and-a half later they had to give me another 150 mcg," Crossley said.
"They were asking me if it had done anything and it hadn't even touched the sides.
"Fentanyl is a strong opiate and as far as I'm aware that was a pretty high dose.
"I was in these spasmodic waves of pain.
"Another hour-and-a half later they gave me 20mg of morphine.
"That was enough to knock me out."
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Crossley was discharged the next day.
Four years later he has no adverse effects from the Irukandji sting, and is working as a diver in Canada.
Highly venomous animals remain 'a mystery' to science
The venom from Irukandji, and its larger cousin the box jellyfish, can cause Irukandji syndrome; a painful, potentially lethal condition associated with a sense of "impending doom".
There have been two confirmed Irukandji deaths in Australia. However, the mysterious deaths of several tourists on the Great Barrier Reef are believed to be linked to the stingers.
Cebrina Nolan, a PhD student studying Irukandji and box jellyfish at the University of Queensland, told 9news.com.au the animals, and their powerful venom, remain a mystery to science.
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"No one really knows how the venom works, we just know the symptoms and what to expect," Nolan said.
"That's what we're now trying to figure out at the University of Queensland.
"The reason why no-one knows, is they're so small and clear they're hard to see. They're only found in certain locations, and their venom is quite unstable."
Nolan explained the methods used to study the venom of terrestrial animals – such as snakes and spiders – doesn't work in Irukandji.
"You can't use them for jellyfish as they're sensitive to organic solvents, which is what we use to purify toxins," she said.
"Plus they're also heat sensitive so they start to fall apart."
Nolan said she's investigating several theories about the venom, explaining it's believed to attack the human nervous system or the immune system – or both.
"We have evidence to suggest that the venom of an irukandji jellyfish, Carukai barnesi, has arthropod-specific toxins that paralyse and kill both crustaceans and insects while the vertebrate specific toxins in its venom allow it to prey, or defend itself, against fish or other animals that may try to eat it," she said.
Irukandji jellyfish are found in Australia's tropical waters, stretching from Bundaberg in Queensland to Geraldton in WA.
National 'hotspots' for stings
While Irukandji are considered relatively rare in Broome, a spate of sightings and stings in recent years has prompted the Shire of Broome to issue messages of caution to oceangoers.
In early 2021 a young boy was lucky to survive a sting in the area, and in November 2019, three beaches in Broome were closed to swimmers following a confirmed Irukandji jellyfish sting.
Parks and Wildlife Service say there are two species of Irukandji that roam the waters along the Ningaloo Coast and Exmouth Gulf.
The first is the Keesingia gigas, which range between 20 to 40 cm in length and are distinguished by a "elongated, cube-shaped bells".
The second is the tiny Malo bella; the species Crossley most likely encountered.
These animals are about the size of a fingernail and "have an elongated tentacle trailing from each of the four corners".
Shire of Broome president Harold Tracey said swimmers need to take adequate precautions when entering northern waters – especially between November and April.
"We encourage everyone to always be cautious when swimming, fishing and launching boats, especially in wet season," he said.
"When there is a beach closure please abide by the no swimming rule and look for and follow all beach signage.
"Please don't become complacent around waterways. Irukandji, crocodiles and sharks are most definitely there, and we need to be vigilant."
Swimmers are advised to wear stinger suits and to always carry vinegar.
There are no records for stings around Broome as most occur during the wet season when beaches are unpatrolled.
However the state's Parks and Wildlife Service at the Department of Biodiversity, Conservation and Attractions (DBCA) does monitor the protected waters around Ningaloo Marine Park and Exmouth, further south.
"So far in 2022, there have been seven stings recorded. The last recorded sting was in July 2022, in the northern part of Ningaloo Marine Park," a DBCA spokesperson said.
"For the Ningaloo Coast, the Irukandji season runs approximately February to July, although stings can occur all year round.
"On the coastline near Broome, stings also occur all year round but can be more prevalent in the wet season, as water temperature increases."
