Imagine a 200-pound man being crushed by the weight of nearly two space shuttles and coming out unscathed. That's about how indestructible the diabolical ironclad beetle is.
The 1-inch-long insect's exoskeleton is capable of withstanding forces up to 39,000 times its body weight. Entomologists who try to mount these beetles for display usually wind up with their steel pins bent or snapped in half.
In a study published Wednesday in the journal Nature, scientists revealed the secrets of this beetle's stab-proof and smash-proof body. An analysis of the beetles' elytra — the hardened casings on top of each forewing — shows that the shields interlock like a 3D jigsaw puzzle and can deform under enormous weight without losing their shape.
Those elytra also fit together with the rest of the beetle's exoskeleton like a suit of armor, making it impervious to crushing forces.
These insights could have applications for improvements to the design of aircraft and armored vehicles.
This beetle can get run over by a Toyota Camry and survive
Whereas most beetles live for weeks or months, diabolical ironclad beetles typically live for two years, mostly in oak trees on the Pacific coast of North America. They can't fly away from danger, which may explain why they developed an exoskeleton that protects them from birds' stabbing beaks and crushing blows.
The researchers behind the study tested how much force the beetle, known as Phloeodes diabolicus, could take without getting squished. The answer: 149 newtons, which means the insect can get stomped on or run over by a car and survive.
"We heard from folklore that you could run them over with a car or step on them, and they don't die. And, of course, we had to try that. So we took a old Toyota Camry and put the diabolical on the ground and ran it over, and it survived," David Kisalius, the lead author of the study, told NPR.
An exoskeleton that locks together like a jigsaw puzzle
Kisalius's group also investigated the beetle's exoskeleton closely using electron microscopes and CT scans. The secret to the beetle's resilience, they found, are a variety of joints that lock pieces of its exoskeleton together.
Imagine the insect's exoskeleton as two halves of a pistachio shell protecting the soft bits inside. The hardened elytra ensconcing its wings are the top half of the shell, and they connect to the underbelly of the beetle's exoskeleton to make one overall suit of armor.
But the various parts of the armor are are joined together in different ways. The researchers found three different types of connections, called lateral supports, between the top and bottom halves of the beetle's exoskeleton.
Each support serves a different purpose in protecting the beetle.
"The strong and stiff interdigitated supports are used to protect the beetle's vital organs from being crushed," Po-Yun Chen, a materials scientist from National Tsing Hua University in Taiwan who wrote an accompanying Nature article about the findings, told Business Insider. "Whereas the compliant latching and free-standing supports allow deformation of the exoskeleton, so that the beetle can squeeze into crevices in rocks or tree bark."
That variation in joint type "is absent in other beetles, which have only interdigitated supports throughout their bodies," according to Chen.
However, cockroaches also have the ability to change their shape to fit into and move within tight spaces, he said.
Insights from this beetle could help us build better vehicles
The researchers discovered that the beetle's elytra, too, are made of pieces that interlock. On top of its wings, they found a rigid joint called a suture that fuses the elytra together like two 3D puzzle pieces nestled together, as shown below.
The interlocking pieces of that suture, called blades, have multiple layers. As the scientists increased the forces on the beetle, those blades broke layer-by-layer, which prevented the suture from snapping all together.
Learning how to mimic those multilayered blades could help engineers design better ways of joining materials. By using the beetles' blades as an inspiration, for example, scientists could create tougher joining materials that won't fracture apart unpredictably, Chen said. Or perhaps they could use the design to keep joints from degrading way that the adhesives, bolts, and pins used in aircraft do.
"When you bring two metals together, it's usually the joints that fails," Aura Gimm, a program officer with the US Air Force office of scientific research, told NPR.
The new research, in fact, is part of an $8 million project funded by Gimm's office that looks to create new impact-resistant technologies that mimic the natural armor of animals.
Chen said the different types of supports the study authors observed on the beetle could be incorporated into armored vehicles, too.
Some of that biomimetic design is already happening.
In 2016, US defense contractor BAE Systems announced a new type of bendable suspension system inspired by the diabolical ironclad beetle, which could allow military vehicles to weather landmine explosions unscathed.
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