The most recent death of 20-year-old German tourist Saskia Thies came last night when she was stung by a box jellyfish at Lamai beach on Samui. Two earlier deaths occurred at Phangan, a popular destination for people attending full moon parties.
Tonight Lisa-ann Gershwin, Director of the Australian Marine Stinger Advisory Services, suggested that nets might be needed to protect swimmers at the popular Thai holiday islands in the Gulf of Thailand.
Last night's stinging death was the fourth box jellyfish sting incident on Samui this year, officials told Phuketwan, but the first death.
Samui and Phangan both depend heavily on tourism. The possibility of box jellyfish, one of the world's most toxic creatures, expanding in larger numbers into that region is something marine biologists will be examining over the next few days.
''Given that this [latest tragedy] and the fatality a couple of months ago were both at night, I'm wondering if there were lights there, attracting the jellyfish?'' Ms Gershwin asked.
''Their attraction to light is well documented, and very very strong.
''If there are lights, it would be imperative to either ban swimming there at night, or install protective procedures or nets or the use of protective clothing. Otherwise you would have a situation where you are literally attracting box jellyfish to the very same place you are inviting people to swim.''
I visited Samui last month, staying at a resort on Lamai beach, and can vouch for the lights being visible along the beach at night.
Ms Gershwin said it would also be a mistake to presume that swimming was safe during daylight hours.
''Boxies may be found at all times,'' she said, ''but in fact they probably are a bit more active during the day because they can see better, and so can their visual prey.
''During the day they are probably more diffusely located because they are not drawn to any particular light (because sunlight is everywhere). But they well and truly are active during the day, and more often than not, they are impossible to see in the water in any but the most perfectly clear, shallow, full sun conditions.
''Even then it is rarely them that you see, only their shadow. I've been working with them for more than 20 years, and I would not rely on my ability to see them to keep myself safe.''
Ms Gershwin and a team of experts from Australia visited Phuket in 2009 to explain the kinds of risks posed by jellyfish infestations and what to do about them.
As a result, marine officials along the Andaman Sea coast have always taken the approach that tourists must be adequately warned and protected from known threats.
''This event underscores the importance of doing something about the problem,'' Ms Gershwin said.
''At this point, funding has been so poor that we still don't even know the identity of the species responsible. From the very few photos taken by divers over the years, I believe that your main box jellyfish culprit is new to science.
''But this research cannot be finalised without specimens, and the bottom line is that unless we continue to rely on crossed fingers as a research and safety strategy, some money needs to be put to this issue to answer basic identification and safety questions once and for all.
''Some may say that the tourism industry cannot afford to address this problem; I would argue that it cannot afford not to and is playing Russian Roulette by failing to do so.''
Box jellyfish have tentacles that can reach three meters long. The sting is so excruciating that many victims go into shock and drown.
Those who make it out of the water often die from the venom, which quickly attacks the heart and nervous system.
Common vinegar is the only known antidote to the toxicity of the box jellyfish.