The diabolical ironclad beetle can be run over by a car and still live to see another day. Its ability to withstand tremendous pressures that could crush its peers may inspire engineers to copy its tricks, but first up are the scientists with their microscopes, mechanical tests, and computer simulations.
Millions of years of evolution have driven some of our smaller critters to fashion structures that are tremendously strong. One of these is the fantastically named diabolical ironclad beetle (Phloeodes diabolicus) primarily found on the western coast of North America beneath the bark of hardwood and coniferous trees.
When the tactic of playing dead by resembling a small rock doesn’t work, the beetle endures the piercing pecks of predators and crushing forces up to 39,000 times its own weight. To put that in perspective, an 82-kilogram (180-pound) person would have to tolerate over 3.1 million kilograms (7 million pounds) of force to perform the same feat of endurance.
"The ironclad is a terrestrial beetle, so it's not lightweight and fast but built more like a little tank," said principal investigator and corresponding author David Kisailus, a University of California, Irvine professor. ”That’s its adaptation: It can't fly away, so it just stays put and lets its specially designed armor take the abuse until the predator gives up.”
A microscopic and spectroscopic investigation revealed the key to the bug’s success lies in the architecture of its elytra — the forewings that protect its delicate flight wings. Despite this, the beetle has lost its ability to fly, the elytra now more a shield than a flight tool. Their forewings are composed of a chitin and protein matrix, with around 10 percent more protein compared to a lighter flying beetle.
Yet there should be a weak point in the beetle’s design: the two elytra join together like pieces of a jigsaw puzzle. This interlocking region should snap at the thinnest part but it doesn’t. To dig deeper, the team visited the Advanced Light Source at Lawrence Berkeley National Laboratory to harness powerful X-rays to get high-resolution real-time data. To confirm their findings, published in Nature, they 3D-printed their own version of the ironclad beetle’s design and ran tests on its strength and durability.
The possible point of weakness where the two elytra interlock instead give way via layered fracturing, which the team calls “a more graceful failure of the structure.” The surface of the wings also feature rod-like elements known as microtrichia, similar to the hair-like protuberances of flying beetles except for the ironclad beetle it likely provides frictional grip to prevent slip during loading.
"This study really bridges the fields of biology, physics, mechanics and materials science toward engineering applications, which you don't typically see in research," Kisailus said. "Luckily, this program, which is sponsored by the Air Force, really enables us to form these multidisciplinary teams that helped connect the dots to lead to this significant discovery."
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