Bizarrely Social and Crafty Octopus Stuns Scientists

Larger Pacific striped octopuses are known for their beautiful stripes and polka dots, and they also appear to be more social than any other known species of octopus. Roy L. Caldwell

Panamanian biologist Arcadio Rodaniche first submitted a scientific description of a bizarre creature called the larger Pacific striped octopus in the 1980s. The animals, which he raised in a large saltwater pool, didn't behave like any other known octopus. They appeared to be relatively social, with males and females sometimes living together in the same den and even sharing food, while also exhibiting other traits unheard-of amongst octopuses and other cephalopods, a group of invertebrates that includes squid and cuttlefish.

But his study was rejected. "Everything Rodaniche was saying about these octopuses was contradicted by the prevailing wisdom of the day," says Roy Caldwell, a biologist at the University of California, Berkeley. "The consensus among cephalopod scientists was that the animals were solitary, with no social behavior that you can think of."

Work on the animal dried up. It's a rarely seen species, found in oft-muddied waters off the coast of Nicaragua, and no scientists came across one for decades. Then, in 2012, along with a biologist at the California Academy of Sciences named Richard Ross, Caldwell tracked down a reputable collector in Nicaragua who had found a few of the animals, which the two scientists took home and raised separately. They then studied their behavior for the next few years and got an additional shipment of the animals in 2013.

Today, the duo, along with Rodaniche and a fourth colleague, Christine Huffard, have vindicated the Panamanian's original work in a study published in PLOS ONE, and the larger Pacific striped octopus does not disappoint: It is a most unusual octopus in several ways.

First of all, it is much more social than any other of its ilk. Males and females sometimes cohabitate and eat together, and also mate beak to beak, all things that are unknown in the octopus world. During copulation, the female appears to nearly envelope the male but doesn't eat him afterward, as is often the cases in other species.

As far as social behavior, most octopuses appear limited to "copulation or cannibalism," says Janet Voight, a cephalopod expert and associate curator at the Field Museum in Chicago, who wasn't involved in the study. "And after copulation, cannibalism is back on the table." But not so with these animals.

A male (left) and a female larger Pacific striped octopus mate. Roy L. Caldwell

Female Pacific striped octopuses will also mate with many males, and sometimes eject the sperm afterward. "They're like, 'Nah, I was just teasing, I'm not using your sperm,'" Voight says. This is the first time this sperm-flushing has been definitely observed in octopuses that Voight knows of.

Aggregations of as many as 40 of the animals have been found in the wild. It's unclear if this means they like to be social or that their specific habitat requirements force them to be together. Regardless, this hasn't been seen with any other octopuses, which tend to be loners, Caldwell says.

Its appearance is also quite striking, with flashy brown stripes and polka dots. But it can also change appearance suddenly, switching from dark red to black to white.

Females of this species live for months after they begin laying eggs. All other known octopus species rapidly begin to die once they brood. But these females continue to live, eat, hunt and mate for months. They also live for a year or two in captivity, longer than most tropical species.

The animal also has some unusual ways of hunting. "They seem to be pretty diverse in their tactics—they drill holes into snails, pry apart clams, probe nooks and crannies with an arm tip to get crabs and other prey," Caldwell says. It pulls off the shell-drilling trick with a hard, ribbon-like appendage called a radula.

When they spot shrimp, though, they have an even more unusual method: They extend a tentacle toward and above a shrimp, before tapping it on the back. The shrimp then tries to escape, right into the octopuses' waiting arms, Caldwell says.

A young octopus reaching toward a shrimp. Roy L. Caldwell

"They track it, they stalk it, like a tiger in the grass," he adds. That's not typical octopus behavior, which usually involves a single pounce as opposed to a calculated and cautious approach.

Caldwell and Ross no longer have the animals in their tanks; their captives all died, and nobody has figured out how to raise the larvae. Caldwell found out he could keep the proto-octopuses alive longer by feeding them larval mantis shrimp but couldn't get them to reach adulthood. The two are hoping their collector will find new specimens soon.

While this species' behavior appears unusual, it's possible that other octopuses act similarly, but we just don't know, Caldwell says. "Most of those 300-some species of octopus have never been seen alive by a biologist or other human, and we don't know anything about their behavior," he notes. He and his colleagues hope this study will help prompt more research in the area.

Frank W. Grasso, a comparative psychologist at Brooklyn College with an interest in cephalopods, says that fact that this species is social could potentially help explain its intelligence and perhaps that of other octopuses (sociality is thought by many to be a prerequisite for intelligence). These social characteristics "might not be unique and might be representative of evolutionary trends that have been suppressed by mainstream science," Grasso says. Are many octopuses more social than we think? It's quite possible, he says.

Jennifer Basil, a biologist who studies chambered nautilus (another type of cephalopod) at Brooklyn College, adds that this "beautifully descriptive work" is a "huge argument for why we need basic research like this. We know so little about what's going on in our oceans, and this is just one example of how one species could have huge implications for understanding the evolution of intelligence."

These octopuses have great vision. Here you can see an "eye stripe" helping to conceal the location of its eye. Roy L. Caldwell