Octopuses are famous escape artists, but how they push their bodies through openings smaller than their own heads had never been broken down step by step. A study published Nov. 5 in the Journal of Experimental Biology used cameras and clear aquarium boxes to show that octopuses follow a repeatable routine: three steps for a roomier hole and four for a tight one.

The researchers also found that two species handled the challenge differently. Young common octopuses adjusted their strategy to fit the opening, while Mayan octopuses largely refused to try the smallest hole at all.

The work has a practical audience — engineers. Engineers designing soft robots for search-and-rescue and ocean exploration want machines that can slip through rubble or reef cracks without a rigid, snake-like body, and octopuses offer a living blueprint.

The Squeeze, Step by Step

The team, led by Wenci Xin of the National University of Singapore, measured the distance between each animal's eyes, which ranged from 15 to 35 millimeters (about 0.6 to 1.4 inches). That width approximates the cartilage capsule protecting the octopus brain, the closest thing the animal has to a skull. Test holes were set either slightly wider than that width or 5 millimeters smaller, according to The Company of Biologists.

Octopuses have no bones, so the brain capsule and the hard, parrot-like beak are the stiffest parts of their bodies. Everything else can deform, which is why the size of the cartilage capsule makes a useful benchmark for how tight a squeeze can be.

With the larger hole, the octopus first explored the opening with its arms. In the second step, it pushed one arm through, usually a front left arm, then threaded up to five more after it. In the third, it reached back with two arms, gripped the wall of the starting box with its suckers, stiffened those arms to push, and pulled the rest of its arms, head, and mantle through. The whole transit took about 20 seconds.

With the tighter hole, fewer arms fit through at once, so the common octopuses split the last step in two. They pulled all their remaining arms through first, then compressed the mantle, the baglike body behind the head, and dragged it through afterward. That fourth step is the adjustment that lets the animal pass an opening narrower than its brain capsule.

Two Species, Two Personalities

Common octopuses, Octopus vulgaris, switched strategies depending on hole size. Mayan octopuses, Octopus maya, behaved very differently, Popular Science reported. Faced with only the small hole, they stayed in a corner without even probing it.

When offered both a small and a larger hole, the Mayan octopuses felt around the small one and then chose the larger passage. The researchers had expected the animals to use the same approach regardless of gap size, Xin said, and the differences suggest there is no single octopus technique for tight spaces.

"Octopuses can change their body shape to squeeze through tiny holes, almost like water flowing through a gap," Xin said. "There is no information about how octopuses squeeze through an opening far smaller than the body diameter."

A Blueprint for Soft Robots

Most robots designed to move through narrow spaces borrow from snakes. "All existing search-and-rescue and exploration robots have slender snake-like bodies, to help them move through narrow gaps," Xin noted. That shape limits how many sensors and tools a robot can carry.

Xin and co-author Cecilia Laschi, a soft robotics pioneer at the National University of Singapore who has worked on octopus-inspired robot arms for years, suggest an octopus-inspired design could carry more equipment in a wider body, then reorganize itself to pass through gaps. Such robots could search collapsed buildings after earthquakes or explore crevices on the seafloor, where rigid machines get stuck.

The octopus routine offers specific engineering lessons. The animals did not force their way through. They tested the opening first, committed one limb at a time, and only then moved the bulky body, a sequence that limits the risk of getting stuck halfway.

In robotic terms, leading with flexible limbs to test an opening, anchoring and pushing from behind, and compressing the bulkiest part last are strategies that can be translated into control software for soft-bodied machines. Video recorded during the trials gives engineers a frame-by-frame reference for each phase of the movement.

Lab Limits and Open Questions

The experiment is peer-reviewed but limited. It tested only two species, both in controlled tanks, and young common octopuses rather than adults. Wild octopuses squeezing into dens or escaping predators may behave differently, and other species may use other approaches. The team also noted a preference for leading with a front left arm but did not explain why, a detail that future studies of arm preference could explore.

The study also suggests the cartilage capsule may partly set the lower limit for how small a gap an octopus can pass, but it did not test holes small enough to find that limit. Why Mayan octopuses avoided the tight hole, whether from body structure, caution or individual temperament, remains unexplained.

The research included scientists from the University of Naples Federico II in Italy and the Haus des Meeres aquarium in Vienna. Aquarium keepers already know the practical lesson well — octopus tanks need tightly sealed lids. The next step, the team suggests, is testing more species and building robotic prototypes that borrow the octopus playbook.

What Readers Want to Know

What did the study find? Octopuses use a three-step routine to pass through holes slightly larger than their brain capsule and a four-step routine for holes smaller than it.

What are the steps? Explore with the arms, push one arm and then several more through, then anchor and push from behind to pull the body through. For tight holes, the body comes through separately after the arms.

Which species were studied? Young common octopuses (Octopus vulgaris) and Mayan octopuses (Octopus maya).

Did both species behave the same way? No. Common octopuses adapted to the hole size, while Mayan octopuses avoided the smallest hole and chose a larger one when given the option.

Why do roboticists care? Octopus strategies could help design soft robots that carry more sensors yet still pass through narrow gaps during search-and-rescue or ocean exploration.

What are the study's limits? It tested only two species in a lab setting and did not determine the smallest gap an octopus can pass.