Researchers used high-resolution microscopic and spectroscopic techniques—even going so far as building a device inside an electron microscope—to shed light on one of the animal kingdom’s most interesting insects: the (aptly named) diabolical ironclad beetle.
The beetle’s exoskeleton is one of the toughest, most crush-resistant structures known to man. You can run an diabolical ironclad beetle over with a car, and it’ll just pop right back up (a la Binx in Hocus Pocus).
In a new paper published in Nature, researchers at the University of California, Irvine dug deep into the material components of the beetle to understand what makes the organism so indestructible and how scientists in the fields of engineering, biology, physics, mechanics and materials science can benefit from this knowledge.
During compression tests, lead author Jesus Rivera, a graduate student in the lab of David Kisailus, discovered that the diabolical ironclad beetle can withstand a force of about 39,000 times its body weight. For context, that is equivalent to a 200-pound man enduring the weight of 7.8 million pounds.
According to the paper, the beetle’s secret lies in its elytra which, in flying beetles, are the forewing blades that open and close to safeguard the flight wings. Being a terrestrial, Earth-bound beetle, the researchers found the ironclad’s elytra has evolved to become a protective shield comprising layers of chitin and a protein matrix. In fact, compared with a flying beetle, the diabolical ironclad beetle's outer layer has a significantly higher concentration of protein—about 10 percent more by weight.
Delving deeper, Rivera and colleagues used CT and scanning electron microscopy to investigate the medial suture that connects the two parts of the elytra together. Under tensile pressure, the researchers saw the connection, which resembles interlocking pieces of a puzzle, give way through layered fracturing rather than snapping at the weakest part.
"When you break a puzzle piece, you expect it to separate at the neck, the thinnest part," explained Kisailus, materials science and engineering professor. "But we don't see that sort of catastrophic split with this species of beetle. Instead, it delaminates, providing for a more graceful failure of the structure."
Kisailus said he sees great promise in the characteristics of the ironclad beetle's exoskeleton, particularly in aerospace, with the development of novel ways to fuse aircraft segments together without the use of traditional rivets and fasteners—which account for stress points on the aircraft.
Kisailus’ lab has already made advanced, fiber-reinforced composite materials based on the beetle’s exoskeleton, joining it to aluminum coupling to determine if it possesses advantages over today’s standard aerospace fasteners. Sure enough, the scientists did indeed find that the beetle-inspired structure was both stronger and tougher than current engineering fasteners.
Beyond aerospace, this biomimickry-inspired research holds implications for any application dependent on tough, impact- and crush-resistant materials.
Photo: A cross section of the medial suture, where two halves of the diabolical ironclad beetle’s elytra meet, shows the puzzle piece configuration that’s among the keys to the insect’s incredible durability. Credit: Jesus Rivera/UCI