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The Dangers of Box Jellyfish in Thailand and Southeast Asia

box jellyfish in Thailand

Box Jellyfish off Thailand’s Beaches

Deadly Box Jellyfish are a Problem in Thailand (But not a major one)

Box jellyfish killed two people off Thai beaches in 2015; the latest being the death of a 20-year-old German woman on Lamai Beach, Koh Samui, in October. Just as alarming, however, are the 11 other, non-fatal attacks in and around Koh Samui and nearby Koh Pha Ngan in recent years.

This sudden surge in stinging cases has officials and hoteliers in Samui and nearby Koh Pha Ngan in a mild panic.  What is happening? Why are there suddenly so many of the dangerous, often deadly box jellyfish in the waters here? Officials are placing bottles of vinegar on safety posts along the island’s beaches and encouraging hotels to invest in nets to keep the jellyfish away from swimming areas.

Koh Pha Ngan, Samui’s sister island just 10 kilometres to the north, and site of the world-famous Full Moon Party, has the sad distinction of having the most deaths by jellyfish in all of Thailand. That’s four deaths in total, in 2002, 2002, 2014 and 2015. The two recent deaths included a young French boy (Aug 2014) and a Thai woman (July 2015).

With so many stinging attacks occurring around these two islands a pattern is appearing in Thailand’s box jellyfish troubles. In total, eight tourists have been killed by the box jellyfish Chironex Fleckeri since records began in the 1990s. Seven of them foreigners with just one Thai.

Tellingly, all but one death occurred in the relatively shallow waters of the Gulf of Thailand. An 11-year-old Swedish girl who fell victim in Koh Lanta in 2008 is the only recorded death on Thailand’s Andaman Coast. Washed by deeper, clearer oceans, this Indian Ocean coastline is emerging as the safer side of the country.

Box jellyfish are known to prefer relatively shallow, calm waters where they are much more pro-active than other jellyfish species.  Many of which are simply swept along with the currents. These hunters of small fish have been observed patrolling back and forth along beaches.  Trailing their long tentacles along clearly navigated paths. Box jellyfish also have rudimentary eyes that allow them to swim around obstacles. With bodies that grow to a square bell about 20  – 30 centimetres across each side, box jellies trail tentacles as long as three metres.

But being translucent, Box jellyfish are near invisible to the human eye, and people can walk or swim right into them even in clear water. And if large numbers of a jelly’s murderous stinging cells wrap around a human torso, a quick death is the common result.  Often right there on the beach just minutes after emerging from the water.

Those stung on the arms and legs by a Box jellyfish often survive, but suffer hours of excruciating pain and deep welts that don’t heal for months.

Jellyfish vinegar station Thailand

As with the Box jellyfish deaths, the great majority of Thailand’s non-fatal stingings also occurred in the Gulf, particularly around islands. This is becoming a serious concern for hoteliers on Koh Samui, Koh Phangan and Koh Mak, another island in the eastern Gulf with at least four serious stingings, but no fatalities.

Koh Mak was the first island in Thailand where hotels began placing nets along beaches to block the entry of box jellyfish.  A move that seems to have worked, with no new attacks reported in recent years.

But statistics regarding injuries by Box jellyfish in Thailand are thin, and do not answer the questions surrounding the recent surge in stinging attacks. Were all of Koh Samui’s recent stinging cases caused by the  chironex Box jellyfish species? Was the 2015 surge temporary, caused by conditions specific to that year? Or is this a warning sign of things to come.  A dangerous shroud spreading over the island’s happy-go-lucky tourism industry?

Some people surmise that rising ocean temperatures are responsible for increasing numbers of jellyfish in oceans worldwide. Also, some scientists believe that as turtles – which consider jellyfish delicacies – are killed off my man, more of the dangerous jellies, such as Box jellyfish, will survive to threaten humans.

The August 2014, Box jellyfish killing of a 5-year-old French boy on Koh Phangan broke a years’ long ‘safe period’ during which tens of millions of foreign tourists swarmed to Thai beaches without fatal attack by jellyfish, sharks, sea snakes or other dangerous sea creatures.

Several tourists drown on Thai beaches each year, while the dangers on land, mostly posed by fellow humans, are something quite different. An occasional tourist gets murdered in Thailand, while many are killed each year in the inevitable road accidents. And while quite a few tourist deaths are attributed to drugs, Thailand remains a relatively safe country for the average visitor engaging in normal behaviour.

Box jellyfish sting

Statistically, Swimming on Thailand’s Beaches is Safe

Many millions of visitors swim on Thailand’s beaches each year, along with millions more Thais entering the sea almost daily. The eight fatalities recorded in Thailand over about twenty years are therefore, statistically, almost insignificant.

Each year many more tourists die from drowning, drugs and motorcycle accidents, and there are surely many additional causes of death that out rank the miniscule danger from Box jellyfish.

Considering the number of times each tourist swims off a Thai beach during his/her vacation, the statistical chances of a fatal or near fatal encounter with a Box jellyfish has to be one in many hundreds of millions.

Another indicator of the prevalence of dangerous jellyfish in Thai waters is the fact that hardly any Thais, even those living by the beaches, are aware of the existence of such deadly creatures.

Of course the manner in which Thais swim, almost fully clothed, helps protect them, but not fully. Thais also leave the part of the body most vulnerable to stings uncovered, the legs. Most Box jellyfish stings take place in shallow water, close to shore.

In the Philippines jellyfish matters are very different. Here a real awareness of the dangers of jellyfish exists among the fishing communities that make up a huge percentage of the population. If the accepted toll of 20 – 40 Filipinos killed by Box jellyfish each year is realistic, that awareness is to be expected.

More about this, and wider the problem of box jellyfish in Southeast Asian waters at the bottom of this page.

Thailand is Leading the Way in Awareness and Prevention (Sort of)

Thailand has made some strides towards educating local authorities and staff in beachfront hotels in recent years. A particular incident in December 2007 on Koh Mak, in the southeast of the Gulf of Thailand, initiated the first real change.

The four-year old son of Australian journalist Andrew Jones was badly stung by a Box jellyfish, and started screaming horrifically from the shallow water. Luckily his father knew to rush for vinegar.  The best-known treatment for box jellyfish stings. The fast-rising, ugly welts across the boy’s legs were washed in vinegar, but still his breathing and heart ceased as he slid towards death. Happily, fate and good fortune intervened, and the child was resuscitated successfully, and survived.

This Australian journalist then engaged in a years’ long campaign to convince the local authorities and hoteliers in Thailand’s beach destinations to take the Box jellyfish problem seriously. The first aid poles now seen along the beaches of Koh Mak, Koh Kood and a few other places in Thailand are evidence of his positive impact.

Phuket has since held a couple of conferences and meetings to discuss the problem of Box jellyfish in Thailand, and spread awareness of the need for vinegar placement along the beaches. Scattered first aid stations, colourful poles holding bottles of vinegar, have been established along some beaches in Phuket, and in different parts of the country.

On Koh Mak, where the Jones-led crusade began, several resorts now place anti-stinger nets long the beaches in front of the hotels each high season and vinegar stations are located on all beaches.

But this is Thailand, a country where some objectives that seem like must-do, good sense to the Western mind gradually fade, and are soon lost.

In late 2019 I walked almost every beach on Koh Mak and Koh Kood taking care to watch for the first aid poles. Some were still there, all right.  Though the majority of them no longer contained vinegar. Perhaps it was due the fact that the high season was well underway and everyone too busy to replenish them. 

But the hotels were full with tourists swimming and playing in the water, seemingly without fear or complaint. These visitors had little or no awareness of the Box jellyfish issue.

Scuba diving box jellyfish

What Other Jellyfish Species Should Tourists Be Aware of on Thai Beaches?

Thai beaches are visited by a variety of jellyfish species – as are most beaches in the world. They generally come in seasons, or in limited migrations that are poorly understood by scientists. Most, happily, are virtually harmless, or cause only itchiness or minor stings. But their presence can cause alarm.

In 2017 jellyfish warnings were put out along Thailand’s Andaman coast by officials in both the National Parks and Department of Marine and Coastal Resources. The Nation newspaper warned of Poisonous jellyfish crowding Krabi, Phi Phi.

These, the paper said, were large schools of Chrysaora jellyfish off beaches on nearby islands where relatively few people swim. This is a large, bulky species that is easy to spot, and they can be handled safely by the bell. While having some poison, they are not dangerous even if a swimmer were clumsy enough to crash into one. The Department of Marine and Coastal Resources warned tourists to be careful when swimming at beaches in Trang and Krabi as venomous box jellyfish have been spotted there. 

This alarming jellyfish warning was also published by The Nation in June the same year, a month when there are few tourists on the beaches, and even fewer in the rough, monsoon seas.

Officials had reported a jellyfish density of 12 specimens per 100 square metres, a shocking situation had these been the deadly Chironex Fleckeri species. Humans would not stand a chance in a soup so thick with the deadly guys whose many tentacles can trail two metres behind.

But these jellyfish were identified as Chiropsoides buitendijki, a species that the authoritative book ‘Venomous and Poisonous Marine Animals‘ says has no reported deaths to its name.

Pink fire jellyfish were blamed in another warning issued in Krabi in 2018 by National Park Rangers, after several Chinese tourists were stung near Koh Hong, an island northwest of Krabi central. The rangers collected and cleared as many jellyfish as they could, and distributed vinegar to treat stings, which can be painful, but not dangerous. This species, Pelagia panopyra, also appears only occasionally, in swarms, and always during the monsoon season.

The well-known Portuguese-man-of-war jellyfish, known on beaches worldwide, are also occasionally washed up on Thailand’s Andaman shores by monsoon winds. But these, with their bright purple balloons floating on the surface, are easy to spot and avoid. They haven’t been sighted in the more sheltered waters of the Gulf of Thailand.

As Thai officials get to know their marine environment better, and as tourist safety becomes a bigger issue, we are seeing more reports about just about everything. That does not mean there are any more jellyfish than there were in the past, when swimming was statistically quite safe.

However, one thing is for certain, as tourist numbers soar in Thailand, there will be more run-ins with Box jellyfish ( and other species) , more accidents and other mishaps. And even those, which will be well reported via social media and other channels,  will not necessarily indicate that Thailand’s beaches are any more dangerous than in the past, or any more dangerous than those in other countries.

What are the Dangers to Phuket’s Millions of Tourists from Box Jellyfish?

Phuket, by far Thailand’s biggest beach destination, has not suffered any known recorded deaths by Box jellyfish. Luckily, perhaps even surprisingly.

So there’s a palpable sense of complacency about the dangers of Box jellyfish there. But they are known to inhabit the area, particularly the calmer east coast of the island. It’s noteworthy that Phuket has hosted a couple of meetings between officials, hoteliers and international jellyfish experts to assess the potential dangers of jellyfish attacks and educate the locals.

Following one such meeting the local authorities boasted of having established first-aid poles with vinegar on all major Phuket beaches.  However, in March 2016 it was reported that all but two or three of the first aid stations on kilometres of beaches had their vinegar bottles missing or empty. Where were the rest of the stations?

The sense of complacency is not too difficult to understand. Phuket now welcomes over 10 million tourists a year, and the majority of those, we can expect, enter the water at least once each day, sometime many more time than that. It’s been going on, with smaller numbers, since the 1970s.

That accounts for hundreds of millions of swimming sessions, all without serious incident. It appears that the only known Box jellyfish sting is of a Russian Scuba diver suffering a minor sting to the face during a night dive, and he survived without any complications.

Most local people on Phuket remain blissfully unaware of jellyfish fatalities or serious stinging incidents. Drownings? There are plenty of those each monsoon season, and they’re topic of local discussion. Road accidents with tourists wiped out? They’re regular, and many people have strong opinions on the problem. Jet-ski and jewellery rip-offs aimed at tourists? Again, they’re on the minds of many locals who make a living from tourism.

But jellyfish? without a known case in the local waters, they simply don’t register as a real problem.

The Most Diabolical of all Killer Jellyfish is Lurking

This, the most diabolical, mystery killer in the oceans is waiting out there. A tiny jellyfish the size of a human thumb, translucent and almost impossible to see, this is so sneaky and deadly that many people may have been killed by it in the past with nobody knowing.

If eventually proved more dangerous than the Box jellyfish, as some suspect it to be, this would surely be the deadliest killer of all on planet earth. Meet the freakish Irukandji syndrome.

But importantly, you don’t have to come to Thailand to meet the lethal Irukandji jellyfish – they’re found in all oceans of the world, and probably right on your home beach, occasionally; in small numbers.

Irukandji jellyfish

While the collection of statistics of death by Box jellyfish has only begun recently, a second, smaller branch of box jellies has an especially sinister characteristic to keep itself off the records. Tiny and almost invisible, Irukandji jellyfish may have hidden their tracks across the human body so well their victims were listed as having died of heart attack or organ failure

Just one or two centimetres across the bell, and almost transparent, Irukandji jellies tow four little tentacles loaded with death and deception. Where the larger chironex jellyfish leave huge, blistering welts across the human skin that slowly heal into ugly, permanent scars, the Irukandji kind do exactly the opposite.

A sting from these may leave no sign at all, and only a small itch at the time of envenomation. Swimmers may even disregard such minor stings as sea lice, or simply not realize they have been tagged at all.

Following a sting, however, their bodies will soon face a perplexing life-and-death struggle that can baffle the best of doctors.

Half an hour or more after a sting, multiple organs in the victim’s body are suddenly stricken by toxins. Muscle pain, cramps and spasms, vomiting, sweating, breathing difficulties, hypertension and even heart failure follow. Severe cases result in death, often without the victim, the family or doctors being aware that a tiny jellyfish was even involved.

The cause of death may be listed as heart attack, respiratory or organ failure – whichever symptom of the Irukandji’s attack is most obvious to the medical examiner. The tiny pinprick on the skin may never be noticed.

Again, the most deadly of these miniature killers was identified in Australia by researcher Jack Barnes, who allowed himself to be stung, under observation, in his attempts unravel the mini creature’s deadly mysteries. A northern Australian aboriginal tribe, the Irukandji, helped Barnes identify the specific jellyfish causing the havoc in the human body – thus their scientific name, Carukia Barnesi, and that of the startling ‘Irukandji syndrome’ they produce.

Like their bigger box cousins that have caused so many human deaths, the Irukandji jellies are also widely distributed across tropical Asia, and far beyond. This invisible demon of the sea has many cousins spread across the planet, though few are as deadly as the Australian-Asian variety.

Japan has non-lethal box jellies. Every month Waikiki beach in Hawaii is visited by thousands of box jellyfish, eight to ten days after each full moon. The east coast of the USA has had infestations of jellyfish in the cubozoa family, also Box jellies, though their stings are not deadly.  200,000 people are reportedly stung by a jellyfish in Florida each year.

Why Thais Won’t Follow Through on the Box Jellyfish Problem

How to get Thai officials and hoteliers in destinations like Phuket – that have not yet suffered a death – to focus on the problem of Box jellyfish in Thailand before it strikes?

More accurately, we should call it a potential problem. And considering the odds, perhaps one in a hundred million in Phuket, it’s a potential problem of minor importance.

The committed Westerner advocating first aid stations and vinegar on the beaches is not likely to make more than a temporary impact in places like Phuket where jellyfish stings are such a minor danger.

The local authorities and hotel managers might go along with safety measures while the spotlight is on them, but as that light fades they will return to the reality of problems impacting their lives and businesses in the here and now.

Despite that scientists have found numbers of box jellyfish in the murky, shallow water along Phuket’s northeast coast (where almost nobody swims), box jellies will not become a topic of concern until – or unless – someone is stung by a Box jellyfish and killed. On other Thai islands and beach destinations that have yet to be stung, it’s much the same.

Sleepy Koh Mak is statistically one of Thailand’s highest risk areas with several recorded stingings, but no deaths – several years have passed since the last Box jellyfish incident. But that may not indicate that the box jellies have disappeared. In the high season four resorts (out of about 24) place nets off the beach to protect their guests (and guests of adjacent resorts).

Still it’s common to see both Thai and foreign tourists swimming outside the nets, apparently unconcerned, despite the presence of warning notices. Both the memory and the vinegar, it seems, are running dry.

People making a living on Phuket and other islands have enough day-to-day problems on their minds. Let’s hope there are not enough box jellyfish off their beaches to awaken them from this statistically happy slumber.

Things could change in Phuket just as they are now changing in the Gulf of Thailand on Koh Samui and Koh Phangan. It has taken six recorded deaths, and many non-fatal stingings, between these two islands to strike enough fear into officials and hoteliers to initiate serious action. But will this translate into on-going, long-term measures to combat box jellyfish and protect their visitors?

That, surely, will mean copying Koh Mak by placing Box jellyfish nets off major beaches, and warning visitors with plenty of clear warning signs. Then come the accessible first aid poles with bottles of vinegar – hopefully the kind that don’t run dry too quickly.

The good news is that there are now warning posters with first aid advice an d warning signs posted in Thai and English at times of year when Box jellyfish are most prevalent.  An example is below:

Jellyfish warning poster Thailand

Background – Box Jellyfish are Not Newcomers to Southeast Asia

‘Jellyfish rule the world – Scientists warn that jellyfish are taking over the world’s oceans. ‘

Sensationalist press headlines like this from the Global Post in October 2013 would have us believe the world is in imminent danger from these menacing blobs of jelly that pulsate their way through our seas in rapidly expanding numbers.

The polluted, dying seas of northeast China and Japan have given rise to terrifying tales of vast masses of jellies that have overtaken the oxygen-deprived waters. Fishermen often find their nets chock-full of the monstrous Nomura’s jellyfish, semi transparent blobs that weigh up to 200 kilogrammes each.

But the problem in Southeast Asia is not one about the life of the oceans, but life and safety of swimmers. In contrast to the huge flabby beasts of Northeast Asia, the species of serious concern in Southeast Asia are near invisible underwater, and often as tiny as your little toe. These seemingly innocuous creatures, the Box jellyfish, are often described as the deadliest animal on planet earth.

Many deaths by Box jellyfish have occurred right on the beach where the victim was swimming, just two or three minutes after being stung and long before the victim could be rushed to a hospital.

In one report of a Swedish woman killed in Langkawi, Malaysia, in January 2010, the husband is quoted as saying his wife died in his arms, still out in the water, just seconds after being wrapped by the jellyfish’s deadly tentacles. Masses of its deadly and painful stings apparently sent her into shock, causing her heart to stop.

jellyfish warning sign

Box jellyfish Were Originally Seen to be an Australian Problem

Australia’s significant experience with Box jellies, originally called ‘sea wasps’, was responsible for identifying the species and making the world more aware of their potential threat.

Primitive as Box jellyfish appear to us, they surprised researchers when they found it had primitive eyes and something of a brain that allowed it to make ‘decisions’ while actively hunting prey. This is no gelatinous blob just floating around the ocean waiting for a fish to flounder into its tentacles as most ocean jellies do.

Box jellyfish have been recorded patrolling back and forth along the same beach, swimming faster than a man, repeatedly following the same course on its hunt. Its 24 primitive eyes allow it to detect and swim right around objects in the water.  That would probably include people if they did not move and blunder into the trailing tentacles.

Transparent and almost invisible, box jellyfish set a deadly trap for people wading and swimming. Human eyes just don’t catch them. And even if the jelly would prefer to escape, it’s often too late.

Young children have splashed into the trailing death trap while playing in shallow water. Swimmers run into their tentacles, and though occasional, divers have also been stung.

Through the 1970s and 80s there was a misplaced belief that these were strictly Australian residents, and a local Aussie problem. But the reality was a lack of recognition and reporting in Australia’s neighbours to the north. Any number of Southeast Asians may have been killed by jellyfish stings before that, with no-one beyond the local villages hearing about it.

With the number of tourists flocking to the famous tropical beaches of Thailand and neighbouring countries now running into the tens of millions, the number of deaths and severe stings from these silent killers is on the rise. And the reporting is now becoming swift and global.

Australian records show over 70 people have been killed by two families of Box jellyfish in over a century since records began. Despite widespread understanding of the problem down under, and many precautions having been taken, Australia still averages one death per year by this nemesis of shallow tropical seas.

The Stingings Are Not New . . .

With foreign tourists of varied nationalities now becoming victims of Box jellyfish in Southeast Asia, new light is being brought to what was surely an old, but unreported problem. Several scientific sources suggest that a staggering 20 – 40 people are killed by Box jellyfish in the Philippines each year, most being Filipinos among the tens of millions who make their living from fishing and other marine activities among the nation’s 7,000 islands. But records show some foreign tourists have joined those unfortunate statistics too.

Thailand has only recently begun collecting data on Box jellyfish stings and fatalities, with five confirmed deaths occurring over the past 20 years , and probably more. Severe stingings or near-death cases number at least 14. Most victims were foreign tourists swimming or wading in shallow water close to the beach, the typical hunting ground of these silent killers. Thais in remote island communities may have been stung by a Box jellyfish during the same period, with no reporting of the cases.

Most human vs Box jellyfish encounters took place in the Gulf of Thailand, in calmer, shallower water surrounding islands such as Koh Pha Ngan, which is known to be favoured by the box jellies.

There is one sad record from the Andaman Coast, however, where a group of four young Swedish girls playing in the shallows of Khlong Dao Beach, Koh Lanta were stung in April 2008.  This resulted in the death of one of them.  The only recorded fatality on Thailand’s Andaman coast. The deeper, clearer water surrounding most islands here is apparently not as well suited to jellyfish hunting as the shallower, more placid waters within the Gulf.

In its central location in Southeast Asia, Malaysia cannot escape the scourge of the Box jellyfish either, as much as it might want to. There have been accusations of Malaysian officials ignoring the issue for years, apparently in an attempt to avoid negative press reports of Box jellyfish that might hurt their booming tourism industry.

Even private industry in key beach resorts like Langkawi seems reluctant to discuss the problem openly. Here is a report in the Langkawi Gazette about the Swedish woman mentioned above for her reported death just seconds after being stung: 

‘The Chironex Box Jellyfish is well-known ….. at beaches along the mainland in Malaysia, Australia, Thailand, Philippines …… There has been a confirmed sting in May 1996 and a suspected box jellyfish sting in January 2010 in Langkawi. Consequently the likelihood of being stung by this type of Jellyfish in our immediate area is rare’.

At the same time, a report in the Phuket Wan newspaper from nearby rival destination Phuket took an entirely different, more open approach to the same event: Alarm as Box Jellyfish Kills Tourist on LangkawiThe death of a Swedish tourist on the Malaysian island of Langkawi, apparently from a box jellyfish sting, has heightened concerns about swimmers’ safety throughout the region. Swedish media reports have focused on the death, which is likely to alarm some visitors to Malaysia and Thailand.’ At least three deaths by Box jellyfish stings have been recorded in Malaysian waters.

Indonesia, with 17,000 islands lying between Malaysia and Australia, surely has populations of box jellyfish, though there is little news of them. Reports of deaths by jellyfish in distant islands probably wouldn’t travel to any central authority. Bali, the centre-piece of tourism in the country where a fatal incident is unlikely to go unreported, has no records of death by Box jellyfish stings.