They're 300 million years old. They're almost invisible and they are deadly. Cubozoa, Box jellyfish or Irukandji, are both the smallest and the most venomous jellyfish in the world. There are more than 50 species and Dr Karl joins Lisa-ann Gershwin on her hunt for more. When Box jellyfish fire their stingers, the pain and other symptoms are collectively known as Irukandji syndrome and it can kill. But something as thin as pantyhose can save your life - how does that work ? http://lisagershwin.com