The domain of entomology is built on the humble pin: biologists venture into meadows and forests, pick up insects, euthanize them and pin them on the trays that make up the natural history collections of museums and universities, immortalizing thus specimens for future scientists to examine. But the devilish armored beetle – his real name, though more formally known as the Phloeodes diabolicus– will not suffer from such indignity. Native to the southwestern United States, it is known as the “pin-bender,” an insect so tough that when biologists try to ram a pin through its black, bumpy shell, the puny metal gives way. It’s so difficult that entomologists have to drill a hole first and then drive the stake. Which is an additional indignity, think about it.
In fact, the Armored Devil Beetle is so tough that if you run over one with a car, it just rolls away. It can withstand forces 39,000 times its body weight. To actually crush this beetle, it takes 150 newtons of force, which, if you’re not fluent in physics, is 7.5 times stronger than the force you can muster by squeezing something between your thumb and forefinger.
For the University of California at Irvine, materials scientist David Kisailus, the evil iron beetle isn’t just a curiosity – it’s an inspiration. Kisailus and colleagues today publish a paper in the newspaper Nature decode at least part of the mystery of how the beetle can handle such feats of strength. Namely, natural selection invented an ingenious structure that prevents the insect from flattening, a structure that Kisailus began to exploit for inspiration to design new, ultra-strong materials. “We are thrilled because we believe we can look to the aerospace, automotive and sports industries with this kind of design,” says Kisailus.
So, to begin with: what does a beetle in the vast insect world do to resist such forces? Morphologically speaking, it’s the beetle’s elytra – the two hard shells that you see a ladybug open as it spreads its wings and takes flight – that act as its shield. But the Armored Devil Beetle (now known as the DIB) cannot fly and has, over time, fused its elytra and the rest of its exoskeleton, creating a cohesive shell.
“Many large, flightless beetles tend to have this characteristic (being really tough), especially those without strong chemical defenses,” writes Matthew Van Dam, a beetle expert at the California Academy of Sciences, in an email to WIRED. (He was not involved in this new work.) “Other studies have shown that it is a good defense against predation. So the trait likely evolved as a defense against predators.
We might first assume that the beetle incorporates some sort of mineral into its exoskeleton to give it extra strength. It wouldn’t be unprecedented: a deep sea snail, for example, builds an iron shell. But no, the DIB is completely organic. “What we do know is that these are simple organics – there is no mineral, like you would find in a shell that is really resistant to crushing,” Kisailus says. “The beams that hold your highways are concrete for a reason: ceramics are excellent under compression. And yet, there is no mineral in it. Everything is organic. “
So there must be something special about the structure of the exoskeleton: The body should be built in such a way as to absorb the energy with a crushing blow, much like a skyscraper is built to sway slightly during an earthquake to avoid breaking in half . And indeed, Kisailus and his colleagues have found two key evolutionary innovations that make the DIB so tough: lateral supports and a medial suture.