The evil iron beetle is like a small six-legged tank.
The resistant exoskeleton of this insect is so hard that the beetle can survive being hit by cars and many potential predators do not have a chance to crack. Phloeodes diabolicus is basically nature’s jaw breaker.
Analyzes of microscope images, 3D-printed models, and computer simulations of beetle armor have now revealed the secrets of its strength. The well-intertwined, impact-absorbing structures that connect parts of the beetle’s exoskeleton help it survive huge crushing forces, researchers report on Oct. 22. Those features could inspire new, rugged designs for things like armor, buildings, bridges, and vehicles.
The diabolical iron beetle, which inhabits desert regions of western North America, has a clearly difficult shape to ruin. “Unlike a stinking beetle or a Namibian beetle, which is more rounded … it’s under the ground [and] is flat on top,” says David Kisailus, a materials scientist at the University of California, Irvine. In compression experiments, Kisailus and colleagues found that the beetle could support about 39,000 times its own body weight. It would be like a person carrying a stack of about 40 Abrams M1 battle tanks.
Inside the tank-like physique of the evil iron beetle, two key microscopic features help it withstand the crushing forces. The first is a series of connections between the upper and lower half of the exoskeleton. “You can imagine the exoskeleton of the beetle almost like two halves of a shell sitting on top of each other,” Kisailus says. Crests along the outer edges of the top and bottom together.
But these nerve connections have different shapes in the body of the beetle. Near the front of the beetle, around its vital organs, the ridges are very interconnected, almost like teeth with a zipper. These connections are rigid and resist bending under pressure.
The connective ridges near the back of the beetle, on the other hand, are not so intricately intertwined, allowing the upper and lower halves of the exoskeleton to slide slightly. That flexibility helps the beetle absorb compression in a region of its body that is safer to crush.
The second key feature is a rigid joint, or suture, that runs the length of the beetle’s back and connects its left and right sides. A series of protrusions, called blades, fit together like puzzle pieces to join the two sides together. These sheets contain layers of tissue glued together by proteins and are highly resistant to damage. When the beetle is crushed, small cracks form in the protein tail between the layers of each leaf. Those small curable fractures allow the blades to absorb impacts without breaking completely, explains Jesus Rivera, an engineer at UC Irvine.
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This hardness makes the diabolical iron beetle proof of predators. Kisailus says that an animal can make a meal with the beetle by swallowing it whole. "But the way it's built, in terms of another predation, let's say like a bird pecking at it or a lizard trying to chew it, the exoskeleton would be very hard to crack."
That hard exterior is also a problem for insect collectors. The diabolical iron beetle is notorious among entomologists for being so fantastically durable that it bends the steel pins that are commonly used to mount insects for display, says entomologist Michael Caterino of Clemson University in South Carolina. But “the basic biology of this thing is not particularly well known,” he says. “I found it fascinating” to learn what makes the beetle so indestructible.
The possibility of using beetle-inspired designs for aircraft and other more resilient structures is intriguing, Caterino adds. And with the splendid variety of insects from around the world, who knows what other critters might someday inspire cleverly engineered designs.