This volume is full of unexpected revelations, not for the squeamish, starting with the fact that the preferred plural of “octopus” is “octopuses,” not “octopi.” Octopuses, we learn, can lurch onto land and can change color and shape in seconds. After 272 pages in the company of these animals, they no longer seem weird because of their four pairs of arms lined with suction cups. They’re weird because of the ways they contradict our ideas about intelligence.

Even Aristotle got it wrong, although octopuses are, of course, plentiful in Greece (where they’re often served in balsamic vinegar). When he wrote that “the octopus is a stupid creature, for it will approach a man’s hand if it be lowered in the water,” he missed that octopuses are more curious than afraid. Like small children, they grab unfamiliar objects, such as underwater cameras, and seem to embrace and fondle them. They gaze through the glass at visitors to aquariums and, like attentive dogs, watch their researchers.

This is all the stranger since, unlike dogs (or dolphins or bees or humans), octopuses are not social. An octopus is a model of self-reliance. Its mother dies as soon as her eggs hatch, and the father soon thereafter. It lives for six months to five years, depending on the species, without bonding to a mate or learning from other octopuses. No man is an island, but every octopus is. Yet octopuses react to us, turning “black with joy” or “white with anger” in response to human actions.

Why might a loner behave in ways that seem social? One argument is that extreme self-reliance requires extreme engagement with the environment. We associate intelligence with dependence in childhood, longevity, and civilization; but in the case of the octopus, it seems that the opposite conditions promote curiosity, problem-solving, speedy learning, and sensitivity.

Roland Anderson, a retired biologist from the Seattle Aquarium, tells author Katherine Harmon Courage that octopuses are the “smartest invertebrate,” and to prove the point, he lists a set of very human traits:

They are a predator, they go out to find food, they build dens and then modify them, they use tools, they use spatial navigation, they have play behavior, they recognize individual people.

In one experiment, Anderson and his colleagues gave a female giant Pacific octopus named Billy a plastic bottle of herring with a childproof cap. In 55 minutes, she figured out that she needed to push and turn the lid simultaneously and was able to open it; with practice, she could do the trick in five minutes. An octopus can also learn to distinguish vertical from horizontal bars and the letter “V” from “W.” The intelligence of the octopus lies “somewhere in the middle of the birds—maybe not as smart as an African gray parrot,” Courage writes. And birds are an impressive bunch. Many species seem sharper than we once guessed, the author notes, largely because researchers are getting better at reading behavior without imposing a human bias. Still, it’s hard to gauge when imaginative observation is influenced by affection. People who study lobsters, for example, claim that they are smarter than octopuses.

Katherine Harmon Courage reports several tales in which octopuses react to human actions. One researcher describes an octopus pushing up the lid of its tank, apparently trying to get out. The researcher banged on the lid and the animal retreated. The next day, as she sat nearby, the octopus lifted up the lid, brought its funnel to the crack, and squirted a jet of water at her. To test whether an octopus can distinguish between two people, Roland Anderson created a good-cop/bad-cop routine. The bad guy approached a giant Pacific octopus and harassed it with a bristly stick; the good one would come close and feed it. After two weeks, when the bad guy entered the room, the octopus “would shrink back into the corner, it would turn its suckers out to be ready to fight, and it would blow jets of water toward that person,” says Anderson. It also assumed an expression that scientists identify with aggressiveness. When the good cop arrived, the octopus “would come up to the surface or raise its arms up toward the surface,” ready to receive the anticipated food.

Octopuses even exhibit signs of what we call boredom. Trapped in a small, bare tank, they are likelier to throw themselves against its side, to eject ink, or to turn white. When an octopus gets time in a more interesting environment and is then put back in a bare tank, it may eat its own arm.

That need for stimulation may seem surprising in creatures with such a smallish brain; but, upsetting our assumptions again, most of their neurons are in their arms. These jointless appendages have a huge range of motion: too wide, scientists argue, to be subject entirely to centralized control. Octopuses do sometimes stiffen their pliable arms into a three-jointed appendage like ours, perhaps when the brain needs to keep track of them. Thus, the arms are both under the control of the brain and independent of it. Some species can eject an arm, which slithers off and distracts predators to chase it.

A severed arm remains active for some time, as Courage amusingly demonstrates in a story about a Korean restaurant in Flushing, New York, where customers select a live octopus from a tank. (The manager tells Courage that, in Korea, farmers feed raw octopus to sick cows and bulls, which consequently recover from their illnesses in a day.) The octopus meal arrives cut-up but alive, along with plates of dipping sauces: “The muscular arm segments look like little slugs, writhing about, gray and stubby, seething all over one another,” Courage writes. The suckers grip the plate: “Once you do manage to get one of these dang things on your chopsticks, it will likely wrap or suction onto the wood with one end, another end twisting around in the air, as if exploring like a blind inchworm.” Inside the author’s mouth, the suckers grab her gums until she pries them off with her tongue.

Octopus! feels a bit plumped out for length, and the author, a journalist who often contributes to Scientific American, shares too much information about her travel arrangements and upsets as she visits Spanish fishing boats and Italian laboratories. But the prose is enthusiastic, funny, and unpretentious, steering clear of the style of science writing that risks too much metaphor and speculation. The octopus remains intriguing and baffling.

Temma Ehrenfeld is a writer in New York.

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