They are some of nature’s most beautiful villains. Silent. Faceless. Roaming the seas in huge gangs. Yet also fragile and hypnotic, often looking like extra-terrestrial life forms transported from another world. But, of course, what this marine menace is most known for is its infamous sting.

The jelly’s weapon is based around complex cells called nematocytes that line their tentacles (and sometimes bodies), ever poised for both attack and defence. Each nematocyte contains a nematocyst – the stinging element comprising a dose of venom, a tube to deliver it and some form of dart to puncture the skin – or even shell – of the victim. A nematocyst is fired automatically, within microseconds of contacting another life form or even sensing one close by.

But just how dangerous are jellyfish to us? In the majority of cases, a close encounter will cause an intense burst of pain that leaves a red mark, blistering and sometimes temporary numbness. But this is not to downplay the risks that certain species pose: there are, without a doubt, jellyfish out there with blood on their tentacles. In this feature, we set out to sort the true villains from the jellyfish that have been found guilty through association.