# Insects walking on the ceiling **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [September 6, 2000, 10:19pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288 "2000-09-06T22:19:36Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![RickG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rickg/32/5174_2.png) [@RickG](https://boards.straightdope.com/u/RickG)\ **Post date:** [September 6, 2000, 10:19pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/1 "2000-09-06T22:19:36Z")
With regards to this article: [http://www.straightdope.com/mailbag/mflystick.html](http://www.straightdope.com/mailbag/mflystick.html) While I am loathe to raise doubts about an article written by someone who has so magnificently answered other entomology questions, I am skeptical that **suction** is the primary mechanism for sticking to smooth surfaces. Suction cups work by a combination of elasticity, air pressure, and friction. That is, the elasticity of the rubber/latex/plastic tries to restore the deformed cup into a, well, cup. But because the contact is airtight, no air can enter the resulting space to equalize the pressure, and voila, the surrounding air pushes on the cup, holding it against the smooth surface, where friction prevents it from sliding around too easily. The little plastic toys that stick to glass and roll down it work by (AFAI Understand) van der Waals attraction. They are soft and smooth, and so fill in any roughness on (relatively) smooth surfaces, so there is effectively a lot of contact area for the vdW forces to act. Van der Waals forces act even in a vacuum. I would suspect that the smooth pads on the insects feet act more from contact forces than from suction, unless of course they _are_ suction cups–that is, structures that have some restoring force that tries to pull a vacuum. Am I missing something? Rick ---
**Author:** ![dudeX](https://avatars.discourse-cdn.com/v4/letter/d/e19adc/32.png) [@dudeX](https://boards.straightdope.com/u/dudeX)\ **Post date:** [September 7, 2000, 2:51am UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/2 "2000-09-07T02:51:40Z")
There is an article about Geckos I read recently that proved that their stickyness relies on van der Waal forces. They tried their feet in vacuum, on liquid, and other surfaces. An electronmicrograph showed that the feet had many tiny fern like parts to it to give it a very high surface area. If I find a link to the website that made this discovery I will post it. ---
**Author:** ![DaveoRad](https://avatars.discourse-cdn.com/v4/letter/d/bcef8e/32.png) [@DaveoRad](https://boards.straightdope.com/u/DaveoRad)\ **Post date:** [September 7, 2000, 4:53am UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/3 "2000-09-07T04:53:36Z")
My pet tarantula, Zimbabwe (1989-'97), demonstrated that even relatively heavy tarantulas can crawl up smooth glass surfaces. She did this several times. One time, before I secured the top of her converted aquarium, she actually pushed up the lid and escaped down the back, where she lodged in the folds of a map of Zimbabwe displayed there. I rescued her and reintroduced her to her enclosure, but she immediately ran to the side and just hung there, all eight legs on the glass, as if this were the most natural position in the world. Another time, after I’d secured 1/2-inch hardware cloth across the top, she climbed up to this and, rather clumsily losing her footing, fell. (She wasn’t injured.) My understanding is that tarantulas and other spiders, not unlike insects, have hairy pads as well as claws. (The “hairs”, I understand, are actually velvety bristles.) (Note: Zimbabwe was a zebra tarantula (_aphonopelma smithi_), with ancestors in Costa Rica. She had no connexion to Africa, but I just thought Zimbabwe was a really neat name for a tarantula.) ---
**Author:** ![woodja](https://avatars.discourse-cdn.com/v4/letter/w/ebca7d/32.png) [@woodja](https://boards.straightdope.com/u/woodja)\ **Post date:** [September 7, 2000, 1:41pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/4 "2000-09-07T13:41:57Z")
There’s a pdf article and movie of Geckomotion (like locomotion, but vertical) at [http://polypedal.berkeley.edu/KA/presentations/presentations.html](http://polypedal.berkeley.edu/KA/presentations/presentations.html) ---
**Author:** ![Doug\_Yanega](https://avatars.discourse-cdn.com/v4/letter/d/b5e925/32.png) [@Doug\_Yanega](https://boards.straightdope.com/u/Doug_Yanega)\ **Post date:** [September 9, 2000, 9:01pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/5 "2000-09-09T21:01:53Z")
It’s a combination of things with insects. For many of them, the arolium (the apical tarsal pad) is a flexible membrane with muscular attachment, and it probably does work by suction, at least in part. Nonetheless, I think you can also see that Van Der Waals forces can’t work if there’s any intervening air between the pad and the surface - i.e., a vacuum MUST be created in order for this phenomenon to work. In that sense, there’s really not much difference. ---
**Author:** ![RickG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rickg/32/5174_2.png) [@RickG](https://boards.straightdope.com/u/RickG)\ **Post date:** [September 9, 2000, 10:02pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/6 "2000-09-09T22:02:23Z")
> [@](#): > > \*Originally posted by Doug Yanega \* > **It’s a combination of things with insects. For many of them, the arolium (the apical tarsal pad) is a flexible membrane with muscular attachment, and it probably does work by suction, at least in part.** OK. > [@](#): > > \*\* Nonetheless, I think you can also see that Van Der Waals forces can’t work if there’s any intervening air between the pad and the surface - i.e., a vacuum MUST be created in order for this phenomenon to work. In that sense, there’s really not much difference. \*\* Here, I must disagree with you. Having a very small gap between the surfaces is _not_ equivalent to having a vacuum, at least not in the sense that I think you mean. It’s like saying that, to the extent that there are no molecules of common atmospheric gases in the spaces between atoms/molecules in a solid or liquid, there is a vacuum between the atoms of condensed matter. That may be true in one sense, but I don’t think it is germane to the mechanism of sticking in the absence of the “suction cup effect.” As **woodja** has kindly pointed out, the gecko can walk on smooth surfaces _even if there is already a vacuum_ (I’d love to know how they did that experiment, BTW). The suction cup effect creates an area of lower pressure between the cup and the contact surface so that the cup can be held on by the higher pressure air surrounding it. That is, _air pressure_ is the force that holds the cup on the surface. But vdW force is strictly an electromagnetic attraction, which acts, granted, over pretty short range, but is not dependent at all on surrounding air pressure. Maybe I’m being pedantic. I used to teach physics, so pedantry is a bad habit. But I think it’s misleading to talk about pressure forces as if they are equivalent to adhesive forces. Rick ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 10, 2000, 1:00am UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/7 "2000-09-10T01:00:54Z")
As to gecko’s feet in vacuum, I believe that the article referenced by **woodja** said that the feet stick in vacuum, not that the gecko can walk. Presumably, the gecko in question was dead, and not necessarily still attached to its feet. ---
**Author:** ![Doug\_Yanega](https://avatars.discourse-cdn.com/v4/letter/d/b5e925/32.png) [@Doug\_Yanega](https://boards.straightdope.com/u/Doug_Yanega)\ **Post date:** [September 12, 2000, 5:45pm UTC](https://boards.straightdope.com/t/insects-walking-on-the-ceiling/32288/8 "2000-09-12T17:45:32Z")
“Maybe I’m being pedantic. I used to teach physics, so pedantry is a bad habit. But I think it’s misleading to talk about pressure forces as if they are equivalent to adhesive forces.” Granted, and I’m a pedant, too, so no problem there. My point was really only that one can say “the insect foot adheres to the surface because there is no air between the foot and the surface” and be technically correct whether the forces involved are suction, VDW, or a combination. The absence of air is a requirement for both types of forces.