How many hearts does an octopus have?
Guess before you scroll — the answer is below
The answer
3 hearts
An octopus has three hearts and blue blood. Two pump blood to the gills and one to the rest of the body — and that one stops beating when the octopus swims, which is why they prefer to crawl.
How to get close to this number
Reason from the circulatory problem. An octopus has gills that need their own blood supply and a body that needs another, and its blood carries oxygen far less efficiently than ours does. A system with that handicap needs extra pumping, and separating gill circulation from body circulation is the obvious engineering answer — which gives you three.
The blue blood in the explanation is the cause rather than a curiosity. Octopus blood uses a copper-based molecule instead of the iron-based one in ours, which is what makes it blue and also what makes it a poorer oxygen carrier, particularly in cold water. The extra hearts are compensation for a less efficient chemistry.
The detail about swimming is the memorable one: the heart serving the body stops beating when the animal swims, which makes swimming exhausting and is why octopuses prefer to crawl. A count of organs turns out to explain an animal's behaviour, which is the most satisfying kind of biological fact.
Where this number comes from
| Source | National Oceanic and Atmospheric Administration |
|---|---|
| Figure refers to | 2023 |
| Last checked | |
| Unit | hearts |
Numbers move. If this one has drifted from its source, let us know.
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