These are the most venomous jellyfish in the world

The fear of jellyfish can cloud the joy of bathing. And not without reason: some of the animals are so poisonous that entire beaches have to be cordoned off because of them. Exposure to their toxins can have fatal consequences.

They are fascinating animals and beautiful to look at. But you should leave it at that, because even with harmless jellyfish, skin contact can at least hurt a lot. In the case of the poisonous, it is deadly at worst.

All jellyfish are poisonous – and some especially

Has with Prof. Dr. Andreas Schmidt-Rhaesa, employee at the Center for Natural History at the University of Hamburg. He is also a co-author of the recently published jellyfish atlas, World Atlas of Jellyfish. As he enlightens us, the distinction between non-venomous and venomous jellyfish is incorrect. In fact, all jellyfish contain poison – but this is not always dangerous for humans.

Jellyfish are cnidarians. “This group of animals has so-called stinging capsules, and they can explode in response to a stimulus,” says the expert. It would be such a stimulus if you touch a jellyfish. The explosion caused in this way blasts off the cover of the nettle capsule, the nettle threads protrude and bring the jellyfish poison into the skin with a so-called harpoon.

Why jellyfish develop their toxins

There are two reasons jellyfish develop poison at all: defense and prey capture. Consequently, whether or not they require strong venom also depends on a jellyfish’s diet. For example, as an essential part of the ecosystem, jellyfish eat plankton – of course, they don’t need a powerful toxin to do so. However, some species, for example from the group of box jellyfish, are after larger prey such as small fish. A strong poison for catching prey is beneficial here. And this can also be fatal for humans in the event of unwanted contact.

sea ​​wasp

The sea wasp is one of the most venomous cnidarians in the world. According to Prof. Dr. Andreas Schmidt-Rhaesa in some tropical waters, and here likes to be close to the shore. Up to 70 deaths are recorded annually from people who come into contact with it while swimming (e.g. on the north or east coast of Australia).

The screen of the sea wasp is about 30 centimeters long. And from each “corner” of their cube-shaped body emerge tentacles up to three meters long, in which the poisonous stinging cells of the jellyfish are located. Their venom is a neurotoxin that paralyzes their victim’s muscles. As a result, prey fish and crabs can no longer defend themselves or move away, they are eaten in peace and quiet. Contact with their nettles is said to cause people extreme pain, and their highly effective venom literally burns a pattern into the skin of their victims. And depending on which part of the body the neurotoxin acts on, it can (sometimes within minutes) bring death.

Portuguese galley

The Portuguese galley is always washed up on Atlantic coasts, Schmidt-Rhaesa tells us, “for example in Portugal.” But also in the Mediterranean: In April 2021, the Portuguese galley was sighted several times on Mallorca.

Although commonly known as a jellyfish, the Portuguese galley are colonies of individual small polyps that together form a kind of glass dome on the water surface. Their tentacles, which are up to 50 meters (!) long, swim under the surface of the water, and their poison remains on the skin as red, painful welts on contact. In the worst case, it triggers an allergic shock in those affected, which can be fatal if left untreated.

Irukandji jellyfish

It is a particularly small representative of the box jellyfish – when fully grown it barely reaches three centimeters. And yet contact with a poisonous Irukandji jellyfish is not without consequences. The thumb-sized aquatic animals can trigger the Irukandji syndrome in humans, which initially manifests itself with diffuse symptoms such as severe headache, back, abdominal and chest pain. It can also result in severe nausea with vomiting and, in the worst case, life-threatening pulmonary edema.

People in generally stable health should survive Irukandji Syndrome. Before that, however, they have to face quite a path of suffering: a large number of those affected have to be treated in hospital, some of them need opiates in order to be able to endure their severe pain.

Yellow hair jellyfish

The diameter of the screen is already remarkable at around one meter – while the tentacles of the yellow hair jellyfish are up to an unbelievable 37 meters long. The jellyfish is also increasingly found in Europe: You can find them in the North Sea and in the western Baltic Sea as well as in the Atlantic and the English Channel from around late summer.

The yellow hair jellyfish, sometimes called the great lion’s mane, also colloquially goes by the name of its genus: “fire jellyfish”. Skin contact with it is very uncomfortable and leaves a kind of burn that can hurt for a long time – “like a severe sunburn,” says jellyfish expert Schmidt-Rhaesa. Such an injury is rarely fatal.

compass jellyfish

The compass jellyfish is a cannibal: In addition to e.g. B. Fish also have other jellyfish on their menu. Their stinging and sticky pods paralyze and hold prey before being swallowed in a flash and in one go.

In humans, skin contact with the spiral-shaped tentacles causes severe irritation and sometimes allergic reactions. Tricky: The animals, which are already comparatively large (up to 45 centimeters in diameter), like to drift around in packs, making it difficult to avoid them.