What to Know About a Blue-Ringed Octopus Bite

Medically Reviewed by Sabrina Felson, MD on July 16, 2023
Written by WebMD Editorial Contributors
3 min read

A blue-ringed octopus is one of the most dangerous animals in the ocean. Its bite can be fatal to humans. However, very few people have died from a blue-ringed octopus bite. These octopuses are not aggressive and tend to keep to themselves unless they are attacked.

A blue-ringed octopus is one of several species of small octopuses that display small, bright blue rings on their body when they are alarmed. They live in tide pools and shallow reefs. They like moderate-temperature water and are found in the tropics and temperate regions of the world. When they are at rest, they are gray or beige and their rings aren't visible.

Blue-ringed octopuses are tiny. Their bodies are about the size of a golfball and their arms are 3 to 4 inches long. They hide in cracks and under rocks during the day. They eat small crabs, hermit crabs, and shrimp.

While blue-ringed octopuses have extremely toxic venom, they don't make it themselves. They use bacteria they find in the ocean and store it in their salivary glands. The bacteria secrete a toxin called tetrodotoxin, or TTX. It then uses its beak to make a hole in its prey's shell to spit the saliva in it. ‌

The toxin in the saliva paralyzes the prey while the blue-ringed octopus eats it. The TTX that a blue-ringed octopus injects is so deadly that 1 milligram of it can kill a human. It's one of the most potent toxins on earth, and there is no antidote.

TTX does the same to humans as it does to small crabs the blue-ringed octopus eats. It paralyzes you. If you don't receive immediate treatment, all of your muscles will eventually become paralyzed and you won't be able to breathe. The bite itself is very small. It's only a tiny cut that produces at most a drop of blood.‌

You may not even realize you've been bitten until you start to experience symptoms. Some people who have been bitten said that they were conscious and aware of what was going on but weren't able to move. Within 5 to 10 minutes of a bite, you may start to experience:

Not all bites contain the same amount of venom. How severe your symptoms are will depend on how much toxin was transferred into you with the bite. Children and small adults are more at-risk. With severe bites, your symptoms may get worse and include: 

If you are bitten by a blue-ringed octopus, seek medical help immediately. If you are with someone who is bitten, you should:

  • Call emergency services immediately.
  • Keep the person who was bitten as still as possible. Have them lie down if possible.
  • Apply a wide elastic bandage to the bitten area.
  • Bandage the entire limb. Wrap it as tightly as you would for a sprained ankle.
  • Apply a rigid splint to the limb. You can use a branch, a piece of wood, or rolled-up paper if needed.
  • Stay with them and wait for an ambulance.
  • Prepare to perform cardiopulmonary resuscitation (CPR) if needed.

As long as you receive prompt treatment, you will probably completely recover from a blue-ringed octopus bite. You may need help breathing until the effects of the venom wear off. The venom doesn't affect the heart or brain, so as long as you can keep breathing, there usually aren't any long-term problems.‌

Deaths due to a blue-ringed octopus bite are extremely rare. There have only been 3 known deaths. Many more people have been bitten but survived.

Blue-ringed octopuses are not aggressive. They try to avoid confrontation by flattening their bodies. You are only likely to get bitten if you step on them or provoke them. If you see one, back away and leave it alone. If you are in an area where they are common, avoid sticking your hands into crevices if you can't see what's inside them.