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The Assassin's Hand

The Box Jellyfish or Sea Wasp (Chironex fleckeri) is perhaps the world’s most venomous creature. The name is derived from Chiron—the centaur poisoned by the blood of the Hydra in Greek mythology. His name comes from the Greek cheiron, “hand,” and the Latin nex, “a murder” or “violent death”— so “the Assassin’s Hand” is a well-deserved epithet. The jellyfish inhabits the waters of the southwestern Pacific and has been responsible for multiple deaths in the northern Australian waters. Between 1883 and 2007, approximately 77 deaths from C. fleckeri were recorded. However, two more were recently reported in Queensland waters between 2021 and 2022.



Children are at greater risk of death due to their smaller body mass. Although stings may occur anytime throughout the year, the official “stinger” season for the Northern Territory is October 1st until June 1st. The bell or body of the organism is a translucent, box-shaped mass that can grow as large as a 2-gallon bucket (a diameter of up to 20 cm or about 8 inches) with a weight of up to 6 kg (~13 pounds.) The tentacles, as long as 3 meters (almost 10 feet), contain millions of nematocysts that act like “spring-loaded syringes” and release venom when stimulated. Nematocysts fire venom into the skin within 3 milliseconds of being triggered, distributing venom over a large surface area, thus allowing for rapid absorption. The force of this strike is approximately 2–5 pounds per square inch, enough to penetrate the skin’s upper dermis and discharge venom into the microcirculation. Additionally, tentacles contain a sticky fluid that helps bind the tentacle to the victim.


Box jellyfish envenomation syndromes include sudden cardiogenic death, hemolysis, and dermato-necrotic manifestations. Patients stung in the water have intense, burning pain and can die within minutes. A 10 cm (~4 inches) length of tentacle is said to deliver a lethal dose, but this is variable. C. fleckeri venom is thought to produce abnormalities in ionic transport across cell membranes resulting in altered membrane permeability, thus interfering with how nerves and muscles work. Patients may experience initial hypertension (high blood pressure) followed by hypotension (low blood pressure), cessation of breathing, and finally, cardiovascular collapse. Toxic skin reactions from the adhering tentacles include a characteristic crosshatched ladder pattern with subsequent wheals, vesicles, and later necrosis.


In patients with box jellyfish envenomation, immediate emergency measures are required to treat hypotension, and arrhythmias, if present. Some suggest applying vinegar (3%–10% acetic acid) for skin decontamination to prevent the nematocysts from disarming during removal. C. fleckeri antivenom is available for treatment from Commonwealth Serum Laboratories, Australia, and is made using hyperimmunized sheep. The antivenom has been shown in vitro to neutralize the lethal hemolytic and dermato-necrotic effects of both milked venom and whole tentacle extracts. However, efficacy in human envenomation has been debated.

These translucent Cubozoa found floating in the Pacific Ocean expect meals of small fish, marine worms, and crustaceans to become tangled in their long tentacles, not humans. So beware the assassin’s hand, or death may occur “outside the box.”

Adapted with permission from Lily Robinson and the Art of Secret Poisoning.


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