Over 95% of all animals on Earth are invertebrates. The octopus is the smartest of them all and has approximately 300 million neurons throughout its body. That's not much compared to the 100 billion in humans, but it's a giant leap from the 16 million in frogs.
Octopuses are solitary creatures who spend most of their lives swimming alone, even when it comes time to mate.
Some, but not all, types of male octopus will steer clear from a female mate. Instead of getting close, he'll send a package of his sperm to her from a distance, which she'll grab and store for later.
A male will sometimes send a gift along with his package — one of his eight arms, which he severs himself.
Luckily, octopuses can regrow lost limbs, just like starfish. They can even close off the severed artery to reduce blood loss.
When they do bleed, octopuses bleed blue blood, not red. That's because their blood is high in copper instead of iron.
Octopuses will sometimes deliberately sever an arm to distract a predator long enough to jet away at top speeds of 25 mph.
An octopus's brain is located in its egg-shaped head, called the mantle. But the brain does not have complete control over its body. Each arm contains enough neurons to operate semi-independently.
That means each sucker on the arm can decide when it wants to extend, release, and pinch without requiring a command from the brain to do so. That also means the arms will continue to function for a short time after the arm is severed from the body.
A special Korean dish called "live" octopus takes advantage of this fact. The chef will take a live octopus, kill it, chop up the arms and serve them while they're still wriggling on the plate. The dish is often garnished with raw garlic, green onion, and jalapeno.
Octopus is actually highly nutritious: A 3-ounce serving has 139 calories, 2 grams of fat, 25 grams of protein, 45% of your daily iron value, and 510% of your daily B12 value. As Katherine Courage puts it, octopus "totally trumps any chicken."
Octopuses have three hearts. The main heart will actually stop beating when the animal is swimming, so it can't swim very far before tiring out.
And sometimes their hearts will skip a beat. In a 1970s experiment, a male octopus's main heart actually skipped a few beats when a potential female mate was introduced into its tank.
Because swimming is so tiring, an octopus's favorite way of getting around is "walking" along the seafloor. They use their back four arms for walking and their front four to probe for food.
But walking is slow and makes the octopus vulnerable to predators. As a result, some octopuses carry protection with them. Here, an octopus is transporting two empty coconut halves it can hide inside of if necessary.
Octopuses’ most impressive survival tactic is their skin: They can change the color and texture of their skin to blend in with their surroundings and avoid detection. Can you spot the octopus in this photo?
They can complete a full-body transformation in just three-tenths of a second using the three different color-changing sacs in their skin: chromatophores, iridophores, and leucophores. Most other animals who can change color have only chromatophores.
The animals activate different colors by flexing and relaxing the muscles underneath their skin. One scientist documented a single octopus changing colors 177 times within an hour.
Despite their miraculous color-changing abilities, octopuses are colorblind. Scientists aren't sure if the octopus is even aware what its skin is doing when it transforms from one color and texture to the next.
Their skin-changing abilities also make octopuses invisible to unsuspecting prey and therefore makes them effective hunters. Through a lethal bite, they'll administer a neurotoxin to stun their pray. Most of these toxins aren't strong enough to kill a human, but the blue-ringed octopus, although tiny, contains enough venom to kill 26 adults within minutes.
In general, octopuses are not picky eaters: Some of the things found in the stomachs of captured octopuses are shocking: clams, crabs, hermit crabs, lobster, and even seagulls. Check out the poor crab in this photo:
They'll even venture on land to capture their prey. Their strong arms can pry open just about any mollusk shell they come across.
The average octopus has 240 suckers per arm. That adds up to 1,920 suckers total. Each sucker is strong enough to hold 35 pounds.
Octopus suckers are equipped with chemoreceptors which can "taste" their food. It would be like if you were eating pizza and you could taste it the second you touched a slice with your fingers.
Scientists have tested octopuses' intelligence by placing food inside of jars with screwed caps. The eight-armed creatures easily unscrew the jar for the prize inside. One scientist even discovered one could unscrew childproof caps. Now that's impressive!
Just by looking at them, you can see that octopuses are squishy. But you'd never guess just how squishy they can get: Most can squeeze their bodies through any hole that is as large as the only non-squishy thing on them — their mouth, which is a hard beak located at the base of the mantle.
Octopuses live in small dens such as natural rock outcroppings or confined corners in sunken ships. They enjoy decorating these homes with stones and shiny objects. This behavior inspired the popular Beatles song "Octopus's Garden."
Because of their intelligence, octopuses in captivity will get extremely bored and stressed if they're not stimulated. In one study, scientists found that octopuses who spent time in bare tanks began eating their own arms from stress but ceased this behavior when placed in tanks with hiding spots and decorative knickknacks.
Octopuses can even distinguish one human from another. The most convincing evidence for this comes through anecdotes: A certain watchman at the Seattle Aquarium would always shine her flashlight into some of the darkened exhibits, and the giant Pacific octopus residing in one of them didn't like it. So every time that particular guard walked by, the octopus would squirt water on the guard to express its annoyance.
One of the most bizarre and impressive qualities of the octopus is its ability to edit its own genes. Octopuses can alter their genetic code by editing their RNA to become more tolerant of cold temperatures, and they can even improve their eyesight to see better in the dark. Scientists are studying this behavior to potentially learn how to replicate this in humans as a possible cure for disease.
