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Tiny Hairs Help Octopus Suckers Stick

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octopus sucker hair

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Just when you thought octopuses couldn’t get any weirder: It turns out that their suckers have an unexpectedly hairy grip.

Octopuses can form an impressively tight grip—even on a rough surface. And recent detailed microscopic imaging of their suckers revealed an intricate landscape of fine grooves that make these improbable holds possible.

But how do these animals manage to hold their grip—for hours at a time—without getting tuckered out?

A new study, published earlier this month in the Beilstein Journal of Nanotechnology, finds tiny hairs, lining the top interior of the sucker, which might just help enhance the octopus’s hold.

Octopuses are not always on the prowl for food or a mate. And in fact, they spend much of their time hanging out in the safety of a den, where, rather than tread water, they can suction themselves to a wall, ceiling or floor to stay put. But if you or I were dependent on, say, our fingers to hang onto a rocky wall, we probably wouldn’t last too long.

Scientists recently found that the insides of octopus suckers are not a smooth dome, but rather, are crowned by a “protuberance” which juts out, creating a small air (or, rather, water) pocket around it when the sucker is pressed down and activated. This uses the cohesive forces of water to help minimize the energy needed to keep a sucker suctioned—at pressure differences up to 0.269 megapascals (standard air pressure is 0.101 megapascals).

But the new images from scanning electron microscopes found an additional octopus secret: hairs. Tiny hairs. And lots of them.

The researchers imaged the surface of this protuberance in common octopuses (Octopus vulgaris)—both males and females—caught by local fishermen off the coast of Livorno, Italy. The protuberance, they found, to be “completely covered with a dense network of brush-like hairs,” they wrote in their paper. These hairs grew to approximately 50 micrometers long and two micrometers wide. And these main stalks then branched out “into very small filaments” that were closer to five micrometers long and 0.3 micrometers wide. That is to say, much thinner than a human hair.

Scans of the rest of the interior of the suckers showed them to be entirely hairless.

These micro-hairs may help the octopus in keeping an effortless grip on any surface. The hairs “might work in addition to the cohesive forces of water, assisting in keeping the original orifice closed for extended periods of time and significantly increasing the resistance,” the researchers noted. A blend of hairs, water and mucus (all of which the octopus seems to have) seems to boost viscosity where the top of the sucker meets a surface.

A mollusk relative, the abalone, as well as clingfish, also uses microscopic hairs to improve its suction, the researchers noted. And all three of these underwater animals lack the strategy of clingy land animals, such as the gecko, which have been found to have different micro projections—known as setal structures—on their feet. This suggests that “biological structures operating underwater cannot exploit filament-like structures to generate van der Waals forces” (which relies on the creation of electrodynamic pull between molecules), the scientists wrote.

Lab tests have shown that creating fiberous surfaces improves attachment underwater by 20 times—and 25 percent more force is needed to pull them off—over flat surfaces. Considering the substantial interest of engineers in this biological system,” the authors wrote, “our findings may provide an interesting idea for improving the adhesion capability of artificial devices.”

So, the robot octopus uprising might prove to be a rather hairy affair.

Read more about the weird biology of octopus suckers in Octopus! The Most Mysterious Creature In the Sea.

Illustration courtesy of Ivan Phillipsen


Katherine Harmon Courage About the Author: Katherine Harmon Courage is a freelance writer and contributing editor for Scientific American. Her book Octopus! The Most Mysterious Creature In the Sea is out now from Penguin/Current. Follow on Twitter @KHCourage.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. SJCrum 6:03 pm 05/19/2014

    For a little information about the subject of this article, the hairs around the “suction” cups isn’t for the purpose of helping with adherence. in fact, it is the exact opposite of that, and to help break the “suction”.
    As for suction, the real cause of the adherence is that the atoms in the cups has a reverse magnetic charge that either repels, or attracts, the items that are touched. The opposite charge types of things are then adhered to. By the way also, lizards that seem to have sticky feet, and can crawl up walls, etc., are the same exact thing.
    So, the real issue is how to the little hairs help to let go of the “whatevers” they are attached to?
    So, what do you think the little suckers do to let go of the whatevers they don’t want to hold onto any longer?
    Really fun, huh? It certainly can be.
    Well, maybe we can have fun with figuring this somewhat sticky thing also. Go for it, if there are any who would like to have fun with this one also. And, I will give some clues if needed on this one also. It’s better though if you can figure it out yourselves. It’s more fun that way.

    Link to this
  2. 2. SJCrum 5:53 pm 05/20/2014

    As for a clue as to how the itty bitty hairs can cause something to be “dropped” from the suction cups, a clue is that the hairs have to interfere with the same magnetic charge attraction of the cup atoms and those of everything they grab.
    So, how could hairs cause that to occur?
    A second clue, since that one isn’t all that great as far as being fun, is that no, the hairs don’t tickle enough to cause the octopus to let go. So, that’s not it either.
    As for this item it seems like there isn’t much interest in many others, so I will just describe what is involved.
    The suction cups are not a suction type at all, even though they look that way. If they were a suction type they would stick to their own skin. So, that isn’t the right science.
    As for what the “cups” do, is the outer ring has a hole in the center to make all of the outer area have a negative magnetic charge, and the hole helps to spread it out and make it circular.
    The point of the negative magnetic charge is that the “cups” can stick magnetically to all positive charged items. Since its own skin has a negative charge it doesn’t stick to that.
    As for the hairs, when something grabbed is to be released, the octopus’s body sends a positive charge into the hairs, and this then causes enough of a sameness of charges between the positively charged object to reduce the attraction and then let the octopus pull its tentacle away.
    So, that is what the hairs do.

    Link to this

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