See how octopuses squeeze through tiny spaces

A study published in the Journal of Experimental Biology has revealed the precise strategies octopuses use to navigate extremely narrow openings, with potential applications for search-and-rescue robotics. Lead author Wenci Xin, a mechanical engineer from the National University of Singapore, collaborated with coauthors from Italy and Austria, including biologist Tamar Gutnick of the Vienna Zoo, to conduct experiments at a public aquarium in Vienna.

The researchers tested three subadult common octopuses (Octopus vulgaris) collected by fishermen in France and four juvenile Mexican four-eyed octopuses (Octopus maya) raised from eggs in the lab. Each animal, roughly the size of an apple, was placed in an acrylic box with a clear partition containing a hole cut to specific dimensions relative to the distance between the octopus's eyes, which serves as a proxy for the rigid head capsule size.

When presented with a large hole, common octopuses employed a three-step process completed in about 20 seconds: first exploring with a single arm, then pushing three to five arms through, and finally anchoring with their suckers to pull the rest of their body through. For holes smaller than the eye gap, common octopuses adapted a four-step strategy: after the initial exploration and arm insertion, they "jimmied" their arms through individually before compressing their body cavity and internal organs to follow.

In contrast, Mexican four-eyed octopuses "rejected the small holes altogether, not even bothering to try to squeeze through them, instead sitting (sulking?) in the corner of the box," according to the study. However, they readily used the same three-step method for larger openings.

Gutnick noted the octopuses "appear to have a sense of their shifting size and shape and space." Xin is now working to translate these biological strategies into soft robotics for disaster response. Engineer Mishu Duduta of the University of Connecticut, who was not involved in the research, said the findings strengthen the case for pulling-based robot locomotion over pushing, and suggest a new paradigm for "delicate" robotic work in addition to dangerous, dull, or dirty tasks.