The Sea Wasp or Chironex fleckeri is the most potent in terms of poison. if you touch a Sea Wasp you will most likely die your heart will stop within minutes. This species of Box Jelly fish is one of only three that we know can kill humans. Other Box Jellies can cause Irukandji Syndrome this will make your back hurt make you cramp and have nausea and headaches. These symptoms will set in in about 30 minutes from the sting. Twelve to sixteen species of Box jellies can give this. A fully grown Sea Wasp can kill you so fast you might not have time to get to shore. These Jelly fish are very dangerous you should not swim where Jelly Fish have been sighted because even if it is not a Sea Wasp it can be very pain full if you get stung. If you happen to find yourself in the water with jellies swim away while keeping away from its tentacles.
http://www.jyi.org/issue/the-box-jellyfish-australias-other-marine-killer/
