This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Octopuses are extraordinarily versatile. From walking across the seabed on their eight arms to jetting through the water, manipulating tools and squeezing through unimaginably tight spaces, the flexibility of octopuses almost defies belief.
"Octopuses can change their body shape to squeeze through tiny holes, almost like water flowing through a gap, so their size doesn't always limit where they can go," says Wenci Xin from the National University of Singapore. But no one knew exactly how octopuses maneuver through gaps that are smaller than their bulbous mantles. "There is no information about how octopuses squeeze through an opening far smaller than the body diameter," says Xin.
Michael Kuba (University of Naples Federico II, Italy), Tamar Gunit, Daniel Abed-Navandi (both from Haus des Meeres-Aqua Terra Zoo, Austria) and Xin offered young common octopuses (Octopus vulgaris) and Mayan octopuses (Octopus maya) tight holes to squeeze through and publish their discovery that common octopuses use different strategies depending on the size of the hole in Journal of Experimental Biology. First, Kuba measured the distance between the animal's eyes, which ranged from 15 to 35 mm (0.6 to 1.4 inches) and is a good indicator of the size of the stiff cartilage sheath encasing the octopus's central nervous system, which could determine the dimensions of the smallest hole that an octopus can negotiate. Then, Xin designed individual Perspex boxes—some with a hole slightly wider than the distance between the octopus's eyes and others that were 5 mm (0.2 inches) smaller—for the individuals to extricate themselves through.
Filming the escapologists, the team realized that the octopuses used different strategies depending on whether the hole was small or large. When the hole was relatively spacious, each octopus first explored the hole with its arms before popping one through—usually one of the two front left arms—and then threaded up to five of the remaining arms through after. Then, the octopuses reached back with two of the arms that had already passed through, adhering to the partition with their suckers before stiffening and extending the arms to push on the partition and pull the remaining arms, head and mantle through in 20 s.
However, when confronted with a smaller hole, there was a limit to how many limbs the common octopuses could thread through. At that point, the octopus broke the final maneuver into two stages, pulling the remaining arms through the aperture, before compressing the mantle slightly and dragging it through after. Xin admits that he was surprised that the common octopuses used the alternative strategy when negotiating the tightest gaps as the team had thought the octopuses would always use the same approach, regardless of gap size.
However, the Mayan octopuses didn't even try negotiating the tighter hole; they simply sat in the corner of the box and never explored the aperture with their arms. But when they were offered the choice between a small and large hole to escape through, the octopuses initially explored the smaller hole, before abandoning it and emerging through the larger aperture. Having figured out how octopuses negotiate gaps smaller than their bodies, Xin and Cecilia Laschi (National University of Singapore) are keen to take the lessons learned from the octopuses and use them in soft-bodied robots that search ruins in disaster zones and explore the open sea.
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