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In answers to What kind of hot pink eggs are these? and the linked duplicate I found out that snails that live in the water will climb up a smooth stick or branch to deposit their eggs. Today I saw several large (8 to 10 cm) snails climbing trees both a relatively smooth one and one with considerably rough bark.

How do these large and heavy snails manage to adhere safely to the sides of trees and climb so high? Is it adhesion? Is suction involved?

10 cm snail climbing a tree 10 cm snail climbing a tree 10 cm snail climbing a tree

click images for full size view

above: June, northern Taiwan lowlands in a damp area. They look similar to the species discussed in answers to What are these four large snails doing? below: from What kind of hot pink eggs are these?

hot pink snail eggs

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The foot of the snail secretes a sticky mucus which allows the snail to climb even the smoothest surfaces. The mucus have two states: one in which it is almost liquid to lubricate motion, and the other - a very viscous one, in which the mucus is sticky and "glues" the snail to the surface. The mucus can alternate between these two states via the pressure the snail activates on it. The gluey state sticks the snail to the surface via adhesion.

Researchers discovered nearly 30 years ago that snail mucus has some unusual properties. It allows the animal to stick to a surface while moving, with the mucus changing its characteristics according to how firmly the snail presses on it. The slime initially acts like glue, sticking the snail to the surface. But when the snail's foot presses down hard enough on the mucus, it becomes more liquid, allowing it to flow underneath the moving snail. Existing theories assumed that this special characteristic of snail mucus was always necessary for the snail to push off and move forward.

Cited from: https://news.stanford.edu/news/2011/april/snail-slime-trails-040611.html

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  • $\begingroup$ How does it alternate between these two states? Does this information come from some source? $\endgroup$
    – uhoh
    Jun 14 '20 at 8:39
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    $\begingroup$ It comes from Prof. Joseph Heller's Land Snail monograph, which I don't have with me right now. See also the following research: news.stanford.edu/news/2011/april/… $\endgroup$ Jun 14 '20 at 9:35
  • $\begingroup$ I didn't see your comment until now for some reason, it may be that the @reply was necessary. From FAQ see How do comment @replies work? I'm still looking for an understanding of the mechanism that holds these snails against gravity from falling off the trees; is it adhesion, or suction, or a combination of both, or if something else is also involved, so I've added a bounty. $\endgroup$
    – uhoh
    Jul 19 '20 at 5:53
  • $\begingroup$ @uhoh The sticky mucus works as a glue, that is: as an adhesive. See en.wikipedia.org/wiki/Adhesive $\endgroup$ Jul 19 '20 at 14:05
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    $\begingroup$ @uhoh I added it to the answer. $\endgroup$ Jul 23 '20 at 12:34

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