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Eight Strange and Wonderful Facts About Octopuses

Octopuses are one of those animal groups that beat science fiction to the punch: big-eyed, multi-armed, soft-bodied, shape-shifting and venomous, with intelligence that can match wits with us; alien, yet homegrown during the Earth’s Late Jurassic period, about 140 million years ago.

Today 300 or so species are distributed among temperate, subtropical and tropical waters around the globe and occupy habitats from coral reefs down to the ocean floor.

Join us to ponder eight stranger-than-fiction facts about octopuses (and yes, that’s the correct plural).

Blue bloods

Octopuses have blue blood. Not from royal genes, but from copper. Unlike a lot of other marine invertebrates, octopuses have a high metabolic rate, and therefore a high demand for oxygen. Copper-based hemocyanin is more efficient for transporting oxygen at low temperatures and low oxygen concentrations than is the iron-based hemoglobin that makes our blood red.

Three hearts

Octopuses also have three hearts: two just to pump blood through the gills and one more to circulate it to the organs. The circulating heart stops beating while an octopus swims, which explains why these cephalopods prefer crawling: Swimming exhausts them.

Giant Pacific octopus can propel themselves through the water at speed, their spear-shaped body leading with their tentacles trailing after.

Ink jet

Sometimes, however, you’ve got to move fast. Many octopuses are able to escape danger by releasing a squirt of obscuring ink as they zoom away on a jet of water. Within their ink sacs they produce melanin, the same dark pigment that’s in our hair and skin. The ink also contains tyrosinase, a compound that burns predators’ eyes and temporarily paralyzes their senses of smell and taste. Altogether, octopus ink is a triple whammy of defense, but it is not poisonous.


On the other hand, all octopuses (plus all cuttlefishes and some squids) are venomous, although only the little blue-ringed octopus of Australia is dangerous to humans. Injected as an octopus drills into its prey with its beak, the venom fatally paralyzes an animal that could otherwise injure the squishy invertebrate in a struggle. It also begins the digestive process. Researchers have discovered that octopus venom contains proteins similar to those produced by pufferfish and porcupinefish as well as by some venomous snakes.

A giant pacific octopus sits on the bottom of its rocky habitat with its tentacles splayed out and its bulbous head lifted.
The giant Pacific octopus can change the color and texture of its skin, going from smooth and red to spiky and mottled brown and white to blend into its habitat or communicate.

Color coordination

Octopuses, along with squids and cuttlefishes, are masters of camouflage, literally changing color, brightness, pattern and even texture in a flash to hide in plain sight or advertise for a mate. This chromatic virtuosity puzzled scientists because, comparing cephalopods’ eyes to ours, they should be color blind. Unlike humans, who have three types of color receptors to see combinations of red, blue and green, cephalopods have only one kind. Looking more closely into octopuses’ dumbbell-shaped pupils, however, researchers hypothesized that the pupils are like prisms that break white light into the separate colors of the rainbow. By changing the shape of its eyeballs, an octopus can bring different wavelengths, or colors, into focus.

An octopus has eight arms, each covered in hundreds of independent suckers, which can feel and taste anything that the octopus encounters.

Multitasking arms

Like eight handmaidens, an octopus’s arms can perform separate tasks simultaneously thanks to a large nerve cluster, like a minibrain, at the base of each controlling its movement. The curling and unfurling arms, dotted with more than 2,000 individually moving suction cups, contain two-thirds of the animal’s neurons. The suckers are equipped with chemical sensors that not only feel, but taste and smell as well. So while an octopus concentrates on hunting, its arms are moving it forward, testing the water and ocean floor, probing coral crevices and maybe even prying open a clam already caught.


Octopuses are standouts in the cephalopod crowd, and among all invertebrates, for their large brains. They can navigate mazes, solve problems, remember, predict, use tools and take apart just about anything from a crab to a lock—all but that last one sophisticated hunting behaviors. Shedd’s aquarists provide our resident giant Pacific octopus with stimulating activities (and enable it to participate in its own wellness care) through regular training sessions that apply the same positive-reinforcement techniques used with the marine mammals. They also offer the octopus enrichment, including a variety of toys and favorite treats, the latter sometimes given as “prey puzzles” in screw-top jars.

It came from the tide pool

Octopuses can come ashore. During short nocturnal forays at low tides, a few coast-dwelling species appear to hunt for easy pickings such as crabs, shellfish and, according to some reports, harbor rats. But with their high oxygen needs, and the extreme exertion of moving their boneless bodies against gravity’s drag, they can only survive on limited gas exchange through their moist skin for a few minutes before crawling back into the sea.

—Karen Furnweger, web editor