The Ancient Art of Folding

Origami is a type of paper art which involves the folding of a single square piece of paper into a three-dimensional object without the use of cutting or gluing. This art form is mentioned in documents from the 15th century, but is thought to have originated in Japan around a thousand years ago. Some simple objects can be produced in only a few minutes while more complex objects can take hours of work.

Another type of intricate folding has been around for much longer – over 230 million years: the wing folding of beetles. This folding is performed in order to conceal the hindwings beneath their hardened forewings known as elytra. These two types of folding have recently intersected which has provided a) greater understanding of the beetle’s physiology, b) insight for new human technologies, and c) an inference to a characteristic of the universe we live in.

Researchers are interested in the mechanics behind beetle wing folding as it has potential for application in high tech fields involving satellites and robotics as well as everyday objects such as fans and umbrellas. A team of researchers in Japan[1] investigated the wing folding performed by rove beetles. This particular species of beetle manages to conceal their wings under exceptionally small elytra.

The researchers turned to the art of origami to help describe the manner in which their wings are folded. One of the surprises in their research was that the wing folding was asymmetrical – the left-wing folds very differently than the right-wing. This was surprising because it does not conform to the bi-lateral symmetry one would expect in animals. Researchers have uncovered several other important dynamics necessary for beetle wing folding.

Folds of a rove beetle wing indicated as mountain folds (solid lines) and valley folds (dashed lines)

Beetles are characterized by having forewings which have been heavily sclerotized forming a protective shell known as the elytra. The elytra are regarded as a novel structure among insects as they bear little resemblance to wings of flight. This feature provides a distinct advantage for beetles, but it also comes with a cost. With this protective shell, beetles have been able to utilize niches which other insects cannot access because it would destroy their wings (e.g., burrowing underground, through carcasses, and under bark). With the loss of the forewings, though, beetles lose some flight ability – they are limited in their maneuverability and endurance.

Many insects position their wing back over the abdomen in order to move them out of the way while not in flight. Some insects, like grasshoppers, exhibit some wing folding to make the wings more compact, but the difference between this and beetle wing folding is that it is only along the length of the wing (longitudinal) – something like a Japanese fan. When positioned this way, the length of the wings exceeds the length of the abdomen. Two problems arise here in the case of beetles. Since the flight capability is shifted entirely to the hind wings, the hind wings are substantially larger, and have a length that well exceeds the length of the abdomen. The elytra of beetles, though, only cover the abdomen at most, and some are even shorter. If the elytra are to serve to protect the hind wings of the insect, the wings need be folded not just longitudinally, but transversely as well.

This kind of wing folding presents a unique engineering challenge. Generally, the structural integrity of insect wings is maintained through the rigidity of wing venation. In order to fold the wings both longitudinally and transversely, a reduction in wing venation is required. Structural integrity is further threatened by the presence of permanent creases in the wing material which are necessary for the efficient folding of the wings.

Dragonfly Wing Veins
Rove Beetle Wing Veins

An additional challenge to the success of wing folding is the need for a mechanism to keep the wings in place once they have been folded away. A team of researchers from China and America[2] studying ladybird beetles observed microscopic “hairs” known as microtrichia on the wing surface, the underside of the elytra, and on the upper surface of the abdomen. These microtrichia, which work a bit like Velcro, serve to assist both in the wing folding process and in holding the hindwings in place under the elytra once the wings are folded. These interlocking hairs also help keep the elytra closed despite perturbations they might receive as the insect explores tight quarters.

Microtrichia found on ladybird beetle wing (Sin Jivu, etal., 2018)

Another aspect pursued by researchers are the mechanisms involved in deploying the folded wings. For most insects, wing deployment is a one-time event. Once they emerge as adults from their pupal stage, hydraulic pressure in the wing veins expands the wings while the cuticle is still soft. Once extended, the cuticle hardens and the wings retain a fixed shape. In beetles, however, a different system involving the ongoing movement of fluid in and out of the wing[3] must be used to allow repeated deployment and folding of wings.

In addition to the ability to deploy the hind wings, for flight to occur beetles must also effectively move the elytra out of the way. The elytra have a considerably different shape than wings of flight, and have an articulation and movement which differs as well. Researchers[4] have examined how this movement occurs which involves the separation of the elytra along with a forward and upward rotation.

Elytra rotation (Frantsevich, 2012)

Underlying all of these structural features is the innate behaviors of the insect which quickly and efficiently deploy the wings and later retract them beneath the elytra. To deploy the wings, the elytra must be shifted apart, the wings then unfold using both hydraulic pressure and muscular contractions, and then it must initiate thoracic muscle contractions to begin flying. This takes several seconds. For retraction, the elytra are brought back into place, and deft movements of the abdomen and thorax fold up the wing. In rove beetles, this has been shown to occur in under two seconds! (Watch a video of this – it is very interesting!) All these complex motions must be programmed into the wiring of the hundreds of thousands of neurons which make up the insect’s nervous system.

As an order of insects (Coleoptera), beetle species number in excess of 360,000 worldwide. There is much variation among all these wing folding features within beetles. Such variation could find its explanation in evolutionary processes of random mutation and natural selection, but those same processes seem to be incapable of addressing the ontological problem – how did beetles obtain all these features in the first place.  This quandary is highlighted by the fact that there are no known transitional fossils between beetles and earlier species of insects.

A small sampling of beetles

The wing folding mechanisms of beetles defy an evolutionary explanation because its success as an adaptation relies upon interdependent systems. The elytra would not confer an advantage in regard to flight unless the wing folding process was in place first, but there would be no advantage to this type of wing folding unless the elytra were present. The morphological features would be useless unless they were supported by innate behaviors, but the innate behaviors could not develop unless the morphological features were in place. The small, undirected, incremental changes which underly evolutionary processes have little power in explaining these “chicken-and-egg” type problems.

Several studies regarding adaptation using bacterial models show that mutations which lead to better survival take a path of least resistance resulting in the loss of function of some parts in order to survive rather than develop new complex features[5]. For instance, if the beetle’s elytra had developed prior to the wing folding capabilities, the wings would become damaged and useless. It would be more likely to expect a complete loss of function of the hind wings – to be come one of Darwin’s “vestigial organs”. So, the development of the more complex wing folding mechanisms necessary to preserve flight ability is actually unexpected.

The optimization of wing features including wing vein reduction, hydraulic functions, permanent wing creasing, structure and placement of microtrichia, as well as maintaining the appropriate size and shape of the wing, make the beetle hind wing an example of irreducible complexity. Should one of these features be lacking or suboptimal, wing folding and flight would not be successful – the insect would be left with a structure that is a disadvantage. Each of these features is influenced by different sets of genes, and one would not reasonably expect that all of these constraints could be coordinated by random mutations of all these genes.

From our human experience, we recognize that a tremendous amount of insight, foresight, planning and design are necessary to produce irreducibly complex mechanisms, interdependent systems and programming of input/response information systems. Rather than advocating for random mutations as a means of securing these features in beetles, it seems to me more reasonable to infer some intelligent agency as a better explanation.

While the mechanisms in beetle wing folding infer intelligent agency, they do not identify the intelligent agent in particular. Nevertheless, I think what we can observe with beetle wing folding indicates some characteristics of that agent. It has the ability to be creative and innovative exercising both design and purpose. It has the ability to attune to miniscule details. It has a pattern of intervening in biological history (the beetle is not the sole example of this type of occurrence). Could it be that this same agent has intervened in human history, and has a designing purpose in the details of my life and yours?


[1] Saito, Kazuya, etal., “Asymmetric hindwing foldings in rove beetles”, PNAS 111:46 (November 2014), http://www.pnas.org/cgi/doi/10.1073/pnas.1409468111

[2] Sun, Jiyu, etal. “Effect of microtrichia on the interlocking mechanism of the Asian ladybeetle, Harmonia axyridis (Coleoptera: Coccinellidae), Beilstein Journal of Nanotechnology (2018), 9:812-823, doi:10.3762/bjnano.9.75.

[3] Sun, Jiyu, etal., “The Hydraulic Mechanism of the Unfolding of Hind Wings in Dorcus titanus platymelus (Order: Coleoptera), Int. J. Mol. Sci. (2014) 15:6009-6018, doi:10.3390/ijms15046009.

[4] Frantsevich, Leonid, Double rotation of the opening (closing) elytra in beetles (Coleoptera), Journal of Insect Physiology, 58:1 (Jan 2012), 24-34, https://doi.org/10.1016/j.jinsphys.2011.09.010.

[5] Michael Behe, Darwin Devolves: The New Science About DNA That Challenges Evolution (New York, NY: Harper One, 2019)

1 thought on “The Ancient Art of Folding

  1. This is a great article. Thank you!

    Sent from my iPhone

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    Like

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