Box jellyfish
In Australia (mainly northern; however, box jellyfish can live in subtropical waters as far south as Sydney, with "Carybdea marsupialis" being recorded as far south as Bermagui, Sapphire Coast) the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.
Box jellyfish
In Australia, "C. fleckeri" has caused at least 64 deaths since the first report in 1883, but even in this species most encounters appear to result only in mild envenoming. Most recent deaths in Australia have been in children, which is linked to their smaller body mass. In parts of the Malay Archipelago, the number of lethal cases is far higher (in the Philippines alone, an estimated 20-40 die annually from Chirodropid stings), probably owing to limited access to medical facilities and antivenom, and the fact that many Australian beaches are enclosed in nets and have vinegar placed in prominent positions allowing for rapid first aid. Vinegar is also used as treatment by locals in the Philippines.
The recently discovered and very similar "Chironex yamaguchii" may be equally dangerous, as it has been implicated in several deaths in Japan. It is unclear which of these species is the one usually involved in fatalities in the Malay Archipelago. In 1990, a 4-year-old child died after being stung by "Chiropsalmus quadrumanus" at Galveston Island in the Gulf of Mexico, and either this species or "Chiropsoides buitendijki" are considered the likely perpetrators of two deaths in West Malaysia. Warning signs and first aid stations have been erected in Thailand following the death of a 5-year-old French boy in August 2014. A woman died in July 2015 after being stung off Ko Pha Ngan, and another at Lamai Beach at Ko Samui on 6 October 2015. At least two deaths in Australia have been attributed to the thumbnail-sized Irukandji jellyfish. Those who fall victim to these may suffer severe physical and psychological symptoms, known as Irukandji syndrome. Nevertheless, most victims do survive, and out of 62 people treated for Irukandji envenomation in Australia in 1996, almost half could be discharged home with few or no symptoms after 6 hours, and only two remained hospitalized approximately a day after they were stung.