Octopuses are famously solitary creatures, typically avoiding interactions with their own species, let alone others. Yet, a surprising discovery has shown that these enigmatic invertebrates not only team up with fish but also collaborate with them during hunts, reshaping our understanding of octopus behavior.

Leadership and collaboration are not exactly common in the animal world, but they do exist. African honeyguide birds famously lead humans to wild beehives, where the humans harvest the honey and leave the wax and larvae for the birds. In the savannas of Africa, zebras and wildebeests often migrate together, their different grazing patterns allowing both species to thrive without exhausting the grasslands.

There are also some interesting underwater examples. Groupers and moray eels collaborate in reef environments, with the grouper signaling the moray eel to flush out prey hiding in crevices. And octopuses were also found to engage in collaborative behavior, with not one but several fish species.

In a new study, researchers wanted to see who’s in charge in this dynamic partnership, and what each of the species does — and it all started when researchers spotted an octopus punching a fish.

Who’s in charge?

In 2018 and 2019, a group of scientists spotted a mixed group (octopus and fish) out for a hunt. The hunt seemed to be going well until one fish got out of line. The octopus, seemingly annoyed at the fish, promptly punched it. In response, the blacktip grouper, returned to the group of fish and continued to mind its business.

This intrigued Eduardo Sampaio, who wanted to see who was actually leading the interspecies expedition.

Sampaio and his team captured 120 hours of video during scuba dives, performing sophisticated behavioral analyses on these groups. They found that, remarkably, there was no true leader — the groups are pretty much democratic.

Researchers identified two key types of influence: “pull” and “anchor” dynamics.

A “pull” occurs when an individual moves away from the group and others follow. In contrast, an “anchor” is when an individual resists movement, effectively stopping or slowing down the group’s motion. The balance between pulling and anchoring plays a vital role in determining the group’s movement and success in locating prey.

Interestingly, goatfish are the primary pullers in these interactions, leading the group in spatial exploration. Their ability to corner prey complements the octopus’s unique hunting skills, which involve probing into crevices with its flexible arms to flush out hidden prey. The octopus, while less likely to initiate movement, emerges as the most efficient anchorer, often dictating when the group halts to hunt.

In other words, every participant is pulling its own weight.

Democracy in the animal world

The first striking takeaway is that the animals may truly be collaborating. The goatfish find the prey, while the octopus hunts it.

The octopus’ ability to adjust its behavior based on the actions of its fish partners suggests a sophisticated level of cross-species social cognition. When hunting with fish, particularly goatfish, octopuses adapt their movements and decisions to optimize the group’s hunting success. The octopus is not merely a passive member of the hunting collective; it actively controls group dynamics.

This is where it gets interesting: the octopus sometimes even uses physical aggression — such as punching fish that disrupt the group’s cohesion — to keep the group in line.

Blacktip groupers, ambush predators that don’t contribute much to group dynamics, seem to frustrate octopuses. As a result, these fish are punched roughly half the time during these collaborations.

These findings highlight that octopuses have richer social lives than previously thought. They also have the ability to integrate social information from partners from other species, making decisions that enhance the group’s overall hunting efficiency. This is particularly remarkable given that octopuses diverged from vertebrates more than 550 million years ago, yet they show social behaviors comparable to more traditionally social species, like primates and dolphins.

“I think sociality, or at least attention to social information, is way more deep-rooted in the evolutionary tree than we might think,” said Eduardo Sampaio, a postdoctoral researcher at the Max Planck Institute of Animal Behavior and the lead author of the research.

“We are very similar to these animals,” he added. “In terms of sentience, they are at a very close level or closer than we think toward us.”

Not everyone is convinced

However, other researchers are more skeptical about this collaboration. Jennifer Mather, an octopus cognition expert at Canada’s University of Lethbridge who wasn’t involved in the study, told National Geographic that octopuses come up like a bulldozer, razing everything in their path and scaring animals in all directions. The fish then follow and try to take advantage of the ensuing chaos.

Alexandra Schnell, a National Geographic Explorer and visiting research associate at the University of Cambridge in the U.K. also says the relationship is very complicated, and it’s unclear whether the fish are merely following some signal or whether the octopus-fish group is truly collaborating.

Yet Sampaio and colleagues are confident some group dynamics are at play.

When blue goatfish dominate the group, the collective becomes more mobile, exploring larger areas of the environment in search of prey. The presence of these fish leads to a more dynamic and exploratory group behavior, increasing the likelihood of prey discovery. The absence of blacktips, which act as movement inhibitors, further enhances this exploratory behavior, allowing the group to cover more ground.

A new frontier for animal behavior

These composition-dependent dynamics highlight the importance of each species’ unique predation strategies and abilities. The combination of fish that explore and lead the group with the octopus’s ability to capture flushed prey creates a highly efficient hunting machine. In turn, this collaboration benefits both parties, with the fish gaining access to prey they might not otherwise capture, and the octopus benefiting from the fish’s ability to locate prey.

The implications of this research extend beyond the specific interactions between octopuses and fish. It challenges long-held assumptions about leadership, sociality, and cooperation in animal groups, particularly in multispecies collectives.

Ultimately, the implications extend beyond the specific behaviors of octopuses and fish. As we continue to uncover more about these remarkable underwater partnerships, it becomes clear that there is still much to learn about the intricate social lives of creatures we once believed to be loners.

Journal Reference: Eduardo Sampaio et al, Multidimensional social influence drives leadership and composition-dependent success in octopus–fish hunting groups, Nature Ecology & Evolution (2024). DOI: 10.1038/s41559-024-02525-2