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Insider's Guide to Box Jellyfish in Thailand

Insider’s Guide to Box Jellyfish in Thailand

Swimming in the beautiful islands and beaches of Thailand is truly a magnificent experience—but this can be dampened by a sea critter known as the box jellyfish. You best watch out for this creature as it was reported to have killed tourists in the country.

But what are these box jellyfish, why are their stinging incidences translating to actual deaths and are these deadly occurrences on the rise? If you want answers to these questions, read our insider guide on these local and lethal wildlife.

What are box jellyfish?

The box jellyfish are an invertebrate species that are highly dangerous especially when you’re out for a swim on certain beaches such as those located in Koh Samui (Chaweng, Bophut, and Lamai) and Koh Pangan (Haad and East Rin).

They’re called as such due to their body structure having a cube-like shape with long tentacles trailing them.

There are certain variants of this jellyfish that you should definitely avoid due to their extremely toxic venom: the Chironex Fleckeri (Thailand), Malo Kingi, and Carukia Barnesi (Australia).

Why are box jellyfish dangerous?

As stated earlier, box jellyfish have already claimed the lives of tourists specifically in 2015 when it killed two tourists in Thailand. They are quite dangerous and below are some of the reasons why:

These box jellyfish may look like any other type of jellyfish out in the open ocean. Don’t let their looks deceive you though as they are some of the most venomous sea creatures known to man.

In fact, their entire body is covered in nematocysts, biological booby traps found in their tentacles that can cause major problems if you get exposed to them. These nematocysts are covered with small poison darts full of poison.

If you or any other creature are unfortunate enough to get exposed to this poison, you might experience cardiac arrest, paralysis, and in extreme cases, even death. This can all happen in a span of a few minutes after being stung.

We’re not saying that you should be staying out of the water for good as out of the 50 different species of the box jellyfish only a small number contain venom that is actually deadly to humans.

Aside from being venomous, box jellyfish are pretty fast swimmers. They can swim with speeds of up to 2 metres per second which far exceeds the swim speed of average human beings, especially that of kids.

Compare that to a human’s average sprinting speed of just 1.64 metres per second and you’ve got a marine creature that can outswim you any time of the day. 

Box jellyfish also have great agility especially when they are swimming to their target locations or when navigating certain obstacles in the area to get to where you are. 

This is pretty impressive for a creature that can weigh up to 4.5 pounds and reach lengths of up to 10 feet!

These aquatic creatures also have intricate structures or systems on their bodies which allow their nervous system to develop. This robust system gives them the ability to move more swiftly and simple cognitive tasks such as discerning dark and light.

This means that aside from being quick, they can take the best route to get to you and be agile enough to slip through corals, rocks, and underwater structures just to let you have a taste of that nasty sting.

Box Jellyfish can also be very difficult to spot when you’re in the water. That’s because they’re transparent in colour and can be quite stealthy even when they’re moving in shallow waters.

Plus, this characteristic can make detecting a venomous sting quite difficult to detect at first. This means that you might have already been stung by a box jellyfish and you might not even know it as the poison tends to spread a few minutes after exposure.

What Thai beaches have box jellyfish?

Based on available data, Koh Samui has the highest number of reported box jellyfish incidents that are either fatal or near-fatal. The island also has specific beaches with high incidents of people getting stung which are listed as follows: 

  • Chaweng Beach
  • Bo Phut Beach
  • Lamai Beach

In fact, over the years, the Koh Samui Hospital has recorded a number of box jellyfish cases that have fortunately decreased as the years went by. Statistics for these reported incidents are detailed below:

  • 8 cases in 2020
  • 8 cases in 2019
  • 17 cases in 2018
  • 47 cases in 2017
  • 42 cases in 2016

As you can see, while these incidents may not constitute a health crisis, they are still a cause for concern as these incidents can be quite dangerous and even fatal in some cases. Plus, it can tarnish the image of the island if the media covers them extensively.

Koh Pangan

Koh Pangan may seem like another hotspot of box jellyfish incidents if you look at the reported cases with six reports of stinging by this aquatic creature. Three beaches in Koh Pangan have confirmed incidents– Haad Rin, East Rin, and Khuat Beach.

There are also other beaches with box jellyfish incidents, such as Koh Phi Phi, Koh Lanta, Phuket, and Krabi. Compared to these beaches, the coast of Andaman is supposed to be safer thanks to its deeper waters.

However, you still need to be cautious as Cha-am and Hua Hin, both located in the Andaman Sea, can see a large influx of box jellyfish, especially during the wet season. 

What can you do to prevent getting stung by box jellyfish?

An ounce of prevention is better than a pound of cure and this saying applies to box jellyfish stings as well. Below are some of our recommendations to prevent getting stung by these critters:

Warm waters that are shallow with sandy seabeds usually attract these dangerous species and most experts agree that these box jellyfish become more active once the sun has set. As such, it is highly recommended that you avoid swimming at night.

To protect swimmers in Thailand, the government has set up jellyfish nets on some beaches. This was initiated in 2021 by the Department of Marine and Coastal Resources on Chaweng and Lamai Beaches in Koh Samui.

As such, if you plan on swimming on these beaches (and the ones we just detailed above), then swim within the area that has been cordoned off with these jellyfish nets. This will significantly reduce your chance of getting stung.

Some Thai beaches will have vinegar stands in them and these are for the effective handling and management of box jellyfish stings. If you are injured or stung by this dangerous sea creature, you have a better chance of survival with vinegar treatment.

The great result you get from vinegar is due to its inactivation of the venom and its prevention of the release of the sting’s other toxins. This is especially true for strings coming from specific jellyfish species such as the box jellyfish.

This kind of treatment has been shown to significantly reduce the pain of the sting and will give the injured person a better chance of survival. Make sure that the vinegar stand has a vinegar bottle that is full or you can also bring your own just to be sure!

Dive or lycra swimming suits are very good swimwear that can provide good protection. The good news is you can now go for stinger suits dedicated to protecting you against painful and dangerous jellyfish stings!

There are a few differences between these two kinds of suits and you need to know which one you need to wear based on your planned activity. Wetsuits and drysuits are ideal for water temperatures between 28 to 77 degrees F.

On the other hand, dive skins and stinger suits are ideal for temperatures that are 70 degrees F and above. Both these suits offer great protection as they cover the legs to the ankles and the entirety of the arms.

This is ideal especially if you have young children as they are not that quick to spot jellyfish threats, they aren’t as tough when it comes to withstanding the sting, and they can’t swim as fast in order to avoid getting stung.

There are sunscreens that will also double as jellyfish sting prevention lotion. You should keep in mind that while there are clinical trials that indicate positive results, there is no concrete proof that it can prevent fatal incidents from venomous jellyfish sting.

You can still wear it though, as it can still help minimise the strings coming from other species of jellyfish that are non-lethal.

While you can get immediate medical treatment if you get stung by a jellyfish here in Thailand, some emergency clinics in rural areas might not have the technical expertise to deal with sting injuries.

There’s also the question of post-trauma treatment that will ensure you recover completely from getting stung by a jellyfish. For this, you have to have comprehensive health insurance. 

Having a comprehensive policy will not only ensure that you get top-notch care from some of Thailand’s best doctors but also access to plastic surgeons in case you need to have some skin grafted to address your affected body part.

Medical emergency treatment might not be readily available during the first few minutes of a sting incident. Below are some of our tips to help against box jellyfish stings:

  • You should keep calm and composed and make sure that you’re level-headed as you ask for further assistance and as you take the affected individual from the water
  • Request other people around to get in touch with emergency services who will then transfer the affected individual to an emergency room or clinic while you administer some first aid.
  • Make sure that there is vinegar available. While you can usually get them from vinegar stands, you may have to do some quick thinking if they aren’t and just ask for some vinegar from food shops and restaurants near the area.
  • Next, you then wash the affected area thoroughly using some vinegar. You should do this for around a minute or so to help prevent the release of venom.
  • If there are still tentacles attached to the affected part, don’t scrape it off as it may lead to the further release of venom. Use a gloved hand or a stick to take out any remaining tentacles from the victim’s affected body part.
  • Next, use some hot water to immerse the affected body part. You can also use a hot shower to help keep optimal levels of red blood cells.
  • If at all possible, keep the stung area immobilised and keep it at the same level as the individual’s heart.
  • If an anti-venom serum is available, then promptly administer it to the victim.

Aside from the box jellyfish, there is only one other fatal jellyfish to avoid that has been confirmed lurking in Thai waters. It’s called the Irukandji box jellyfish which you can easily tell from the regular box jellyfish as it only has a single tentacle.

They also have differences in how they affect their victims. Box jellyfish usually kill their victims by massive envenomation resulting in either cardiac arrest or respiratory arrest.

On the other hand, the Irukandji box jellyfish stings usually result in acute myocardial infarction (AMI) which can then lead to drowning. 

This variant of the box jellyfish is much more active during warm months but other species of Irukandji may have different seasonal patterns.


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