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How do beetles fold their under-wings

 
 
Reply Tue 14 Feb, 2017 08:40 am
I have often noticed that beetles with hard outer wings, like lady bugs, fold there wings in several stages after they alight from flight. The under-wings, that are actually used in flight, are of much greater area than the covering wings, and when the wings are first folded the under-wings project outward beyond the wing covers. Then, in a series of small jerks, the under-wings are pulled in. How do they do this? The wings are thin membranes and are not themselves muscular. How could muscles at the wing root cause the membranes to fold, especially when the range of movement is limited by the overlying outer wings. Does it have something to do with friction against the outer wings and/or the thoracic surface?
 
rosborne979
 
  3  
Reply Tue 14 Feb, 2017 02:27 pm
@ClutteredShop,
Good question. I believe beetle wings are hinged at two places so that they can fold back over themselves, but I'll have to check on that.

You are correct that the membranes themselves don't have muscles, but the main wing articulating structures do have muscles and the membranes probably just collapse between the support structures.
ClutteredShop
 
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Reply Tue 14 Feb, 2017 02:59 pm
@rosborne979,
Thanks for responding, Rosborne. Yes, I assume that the membranes have to fold because the only other ways I can think of that they would retract under the outer wings would be for them to shrink uniformly all over, or be rolled up like a window shade, neither of which seem very plausible. ;-).

However, if they fold along certain crease-lines, how could they maintain adequate stiffness in flight? Could the crease be something like a door hinge, that only allows opening in one direction? Also, it seems there would have to be a double fold, an actual pleat, in order for the folding to occur in the confined gap between the outer wing and the body. It couldn't be a folding over like how we might fold a sheet of paper in half, because in that case you need a lot of open space to swing the folding section through.

Also, it would seem that this folding must occur merely by tugging (since pulling is the only action muscles can do), but I can't imagine what attachment points would allow this tugging to fold a pleat into the wing.

There is, of course, still the possibility I mentioned in the original post, that somehow rubbing between to outer wings and the thoracic wall causes the under-wings to get skooshed up.

Any thoughts (or actual knowledge), anyone?
rosborne979
 
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Reply Tue 14 Feb, 2017 05:43 pm
@ClutteredShop,
Origami figures can unfold into quite large structures, and insect wings have stiff chitin support structures embedded. I suspect it's more a matter of fancy folding than anything else.
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rosborne979
 
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Reply Tue 14 Feb, 2017 05:48 pm
Here, check this out, pretty cool... Smile



I don't know how they unfold them. I'm thinking vascular pressure maybe. I doubt there are muscles for that except at the connection to the body.
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rosborne979
 
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Reply Tue 14 Feb, 2017 05:56 pm
Ok, I found several articles which talk about hydraulic pressure as the basic mechanism, which might be the same or similar to vascular pressure. I'm not sure.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj26bqu5JDSAhUBRGMKHcVnCuMQFggaMAA&url=http%3A%2F%2Fwww.mdpi.com%2F1422-0067%2F15%2F4%2F6009%2Fpdf&usg=AFQjCNHkani6g7z6YGQqHP_452pb5UHTqA&sig2=06_h_eY8Vt8HPZEEyE-oBw

Quote:
“This account shows the distribution of elastic elements in hind wings in the scarabaeid Pachnoda marginata and coccinellid Coccinella septempunctata (both Coleoptera). Occurrence of resilin, a rubber–like protein, in some mobile joints together with data on wing unfolding and flight kinematics suggest that resilin in the beetle wing has multiple functions. First, the distribution pattern of resilin in the wing correlates with the particular folding pattern of the wing. Second, our data show that resilin occurs at the places where extra elasticity is needed, for example in wing folds, to prevent material damage during repeated folding and unfolding. Third, resilin provides the wing with elasticity in order to be deformable by aerodynamic forces. This may result in elastic energy storage in the wing.”
ClutteredShop
 
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Reply Tue 14 Feb, 2017 10:22 pm
@rosborne979,
Wonderful videos, and they reveal a lot. For instance, when the wings first unfold the tips remain bent up at an angle for a while, but then they straighten out and remain fairly stiff. It seems like that could be via a hydraulic mechanism (i.e., pumping fluid into hollow veins to straighten them out).

However, my main question is, how do they fold them up again? Sure, they could pump the fluid out again, but that would just make the wings foldable, it wouldn't do the actual folding, which would require some other mechanism. One possibility, which I don't take very seriously, especially after seeing the videos, is that the "hinges" are spring-loaded, and that they spring back into the folded position after the pressure in the veins is removed.

I wonder if a video of quality similar to these but that showed the folding process (from the outside, of course), would shed some light. For instance, if they showed some kind of rhythmic movement of the outer wings or of the thorax, that could suggest a friction-based mechanism that draws the under-wings inward incrementally.

BTW, I'm glad you posted the excerpt from the article, because the PDF didn't open for me.
rosborne979
 
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Reply Wed 15 Feb, 2017 08:22 am
@ClutteredShop,
ClutteredShop wrote:
Wonderful videos, and they reveal a lot. For instance, when the wings first unfold the tips remain bent up at an angle for a while, but then they straighten out and remain fairly stiff. It seems like that could be via a hydraulic mechanism (i.e., pumping fluid into hollow veins to straighten them out).

I noticed that, which is what made me suspect there is a hydraulic mechanism involved.

I looked for videos of the wing folding, but couldn't find any, probably because it's easier to do a slo-mo video when you know where your subject will be, as opposed to chasing it around the room with your fancy equipment hoping to catch it quickly wherever it lands. Smile

It's possible that they don't "fold" their wings at all, but instead just drop the vascular pressure and pull them in and let the folds happen where they do. Or possibly the vascular pressure can actually be reduced to the point where the wings are "sucked" in???
0 Replies
 
rosborne979
 
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Reply Wed 15 Feb, 2017 08:26 am
@ClutteredShop,
ClutteredShop wrote:
BTW, I'm glad you posted the excerpt from the article, because the PDF didn't open for me.

Here, see if this works better:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4013611/
0 Replies
 
rosborne979
 
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Reply Wed 15 Feb, 2017 08:50 am
This might be a clue to the folding process...


This is a different type of beetle which seems to be using its abdomen to fold the end of the wing "up". I'm thinking that with the ladybird beetles (like in the previous videos), they might be using their hind legs to fold the end of the wings up as they tuck them in. This might account for that upward fold which we can see in the original videos.
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rosborne979
 
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Reply Wed 15 Feb, 2017 08:55 am
Here's a long video which shows wing folding. The wing folding part comes late in the video after all the eating and cleaning Smile

https://www.youtube.com/watch?v=UI4m1yqL4II


It looks to me like the Ladybird beetles do something similar to that other species of beetle whereby they expand and contract their abdomen and use the top surface to "scrunch" the wings into place under the shells.
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rosborne979
 
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Reply Tue 13 Jun, 2017 11:11 am
@ClutteredShop,
This article just showed up in ArsTechnica: Ladybugs fold their wings like origami masters

Link here: https://www.sciencenews.org/article/ladybugs-fold-their-wings-origami-masters?tgt=nr

Video here:
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