Octopuses Squeeze Through Holes Narrower Than Eye Gap, Study Finds

Common octopuses can pass through holes slightly smaller than the distance between their eyes, using a sequence of arm and body movements that changes with the size of the opening. That is the finding of a new study in the Journal of Experimental Biology, reported by ScienceAlert.

The researchers say the movement patterns could inform the design of soft robots for search and rescue, which currently tend to be built like snakes.

Who carried out the study and what did they do?

The work was a collaboration between cephalopod specialists from Italy and Austria and engineers from the Advanced Robotics Centre at the National University of Singapore, according to ScienceAlert.

The team closely watched three sub-adult common octopuses (Octopus vulgaris) as they moved through holes of different sizes. They filmed the animals and broke their movements down into what scientists call motor primitives. These are basic building blocks of movement, controlled by the nervous system, that can be recombined into many different actions. The term began in neuroscience and has since been adopted in robotics.

How does an octopus get through a hole?

The method depended on how large the opening was compared with the animal. When the hole was relatively large, the octopuses followed a consistent three-step sequence: probing, shifting their arms, then squeezing through.

In practice, the animal first explored the hole with its arms. One arm went through first, usually one of the front two arms on its left side, followed by up to five of the remaining arms. Then, using two of the arms already on the other side, the octopus attached its suckers to the partition around the hole and pushed against it. That let it squeeze its mantle and the remaining arms through all at once.

With a smaller opening, the authors report, the final stage split in two. The octopus shifted its remaining arms first and moved the mantle through separately afterward, making a four-step strategy.

Why is the head and mantle the hard part?

According to ScienceAlert, getting the head and mantle through appears to be especially delicate. They hold the octopus's vital organs, including its three hearts, its digestive system and a donut-shaped central brain that wraps around the esophagus.

The central nervous system sits in a stiff cartilage sheath. The researchers used that sheath as a yardstick for the size of hole an octopus could be expected to pass through. Even so, the animals used the four-step approach to get through holes slightly smaller than the distance between their eyes. The videos show them deforming the mantle with their muscles as it passes through.

The report also notes that the main limit on an octopus clearing a bottleneck is its hard beak, along with how skillfully it contorts its flexible limbs and mantle.

Why does it matter for robotics?

Octopuses have no rigid skeleton, which lets them deform extremely and move through tight spaces. The authors describe this as a biological answer to one of the most persistent challenges in robotics. They also write that how the animal organizes its arms and body to adapt to such constraints has remained unclear until now.

The team thinks the movements could inspire a new design for soft robots used in search and rescue missions. Those machines currently tend to use a snake-like shape to get through narrow gaps. An octopus-inspired design, the researchers suggest, could allow more sensors and manipulators to be packed in, improving adaptability during missions.

The authors write that the study adds a new potential combination of motor primitives and offers insight into how octopuses adapt to their surroundings. They add that a better understanding of the squeezing strategies offers useful principles for building soft-bodied robots that can use their own physical design to move through complex environments.

What does this mean for the average reader?

For now, the study is basic research on animal movement rather than a finished product. It helps explain why octopuses so often escape tanks through narrow gaps and how they find shelter in cramped spots. It also gives engineers a documented set of movement steps to draw on when they design flexible machines meant for tight, hard-to-reach places, such as those used in rescue work. The study examined three animals, and the researchers describe the strategies they identified as a contribution to that design effort rather than a final blueprint.

Read next
Giant Oarfish Swims With a Ball-and-Socket Fin That Could Inspire Ocean Robots
Spinosaurus Likely Spent Nearly All Its Time Underwater, Study Finds
Squid Rewrite Their Own Proteins on the Fly, and the Scale Is Staggering

Around Prague, based on reporting by ScienceAlert