Most Poisonous Jellyfishes

1. The Box Jellyfish
Location: Australia
 The box jellyfish contains toxins that attack the skin cells, nervous system, and heart. Human victims often go into shock and either drown or die of heart failure before they reach the shore. Survivors of a box jellyfish sting experience pain for weeks and have scarring.

2. Irukandji
Location: Australia
This jellyfish is only 2.5 centimeters in length, making it very difficult to spot in the ocean. It has stingers not only on its tentacles, but also on its bell. Although this jellyfish is very deadly to humans and other organisms, it is also very fragile. If kept in an aquarium, hitting the side of the tank will be too hard and the impact will kill it.

3. The Lion's Mane/Deep Spiderfish
Location: Northern Hemisphere
This species of jellyfish can become very large. One found in Massachuesetts Bay in 1870 was over 7 feet in diameter and had tentacles longer than 120 feet in length. The farther south you go, the smaller this jellyfish becomes. The bigger Lion's Mane jellyfish are deep red in color. As they get smaller, the color fades to a light orange. Each jellyfish can  have anywhere from 480 to 1040 tentacles along with their oral arms.

4. The Moon Jellyfish
Location: Most Oceans
The Moon Jellyfish is on average, 25-40 cm across. Instead of being colorful like other jellyfish, it's translucent. The Moon Jellyfish has many predators and humans in Southeast Asia often like to eat them.

5. Sea Nettle
Location: East and West coast of North America
The sea nettle is semi-translucent and sometimes lacks its reddish-brown strips and small white spots. On average, it grows to be 6-8 inches with four tentacles. In small creatures, its venom often causes death. In larger creatures, the creature is often temporarily paralyzed. This allows the jellyfish time to get away from its predator. In humans, the sting is often moderate or severe and lasts 20 to 30 minutes.