The diabolical ironclad beetle is tough, and not only by name. New research reveals that getting run over by a car is not even a near-death experience for this bug.
The study, led by engineers at the University of California, Irvine (UCI) and Purdue University, found the diabolical ironclad beetle’s remarkable durability is due to two armour-like adaptations in its exoskeleton which have evolved over millions of years.
These are lateral supports, which act like sidewalls and prevent the beetle from being compressed, along with a “medial suture”, which is a permanent closure of the parts of the exoskeleton known as the elytra.
In flying beetles, the elytra protect the wings and can open to allow flight. But the diabolical ironclad beetle does not have wings. Instead, the elytra and connective suture help to distribute an applied force more evenly throughout its body.
A team led by UCI professor David Kisailus first tested the limits of the beetle’s exoskeleton and examined the various structural components by looking at CT scans.
Using compressive steel plates, the research team found that the diabolical ironclad beetle can take on an applied force of about 150 newtons – a load of at least 39,000 times its body weight – before the exoskeleton begins to fracture.
A car tire would apply a force of about 100 newtons if running over the beetle on an earth surface, the researchers estimate. Other terrestrial beetles the team tested could not handle even half the force that a diabolical ironclad can withstand.
Professor Kisailus told the BBC’s Today programme: “First of all, the name ‘diabolical’ gives you visions of something of horror, right? And ‘ironclad’ makes you think it must be incredibly robust. But if you were to look at it you wouldn’t necessarily be able to discern it easily in the field because it actually looks like a small stone.
“And I think that’s probably part of its mechanism of survival – as a bird or a rodent or a lizard wouldn’t want to pick it up and eat a stone. But they would be in for quite a battle.
“It’s not that the beetle is fighting back, it’s just that they’re so tough and so robust it would just stand there and take it.”
Asked exactly how resilient it was, Professor Kisailus said: “If you were to look at it from the side, it looks like a little tank. After we ran it over with a car, we did proper mechanical testing and crushed it in one of our dynamic mechanical testing devices.”
“This beetle which is adapted to living on land, and has these two halves of its flying structures now permanently stitched together by a jigsaw puzzle-like architecture which we call the medial suture.”
Asked how this arrangement could be used to adapt human technology, Professor Kisailus gave the example of the joins between components inside an aircraft, which need to be bonded together strongly, but are also resilient enough to withstand various forces (toughness).
He said: “We thought, ‘Oh, let’s make a mimic of the beetle’s jigsaw-puzzle-like structure and join a metal – a piece of aluminium – with a composite, and let’s pull on it and compare the strength and toughness to that which you would see on an aircraft, and what we found was, the strength of the beetle’s suture – the mimic that we made – was roughly the same strength as the aircraft fastener, but 100 per cent more tough.”
David Restrepo, an assistant professor at the University of Texas at San Antonio who worked on this project as a postdoctoral researcher, explained the concept. He said: “An active engineering challenge is joining together different materials without limiting their ability to support loads. The diabolical ironclad beetle has strategies to circumvent these limitations.”
The scientists said that in the turbine engines of aircraft, metals and composite materials are joined together with mechanical fasteners which can add weight and introduce stresses which can lead to fractures and corrosion.
“These fasteners ultimately decrease the performance of the system and need to be replaced every so often. But the interfacial sutures of the diabolical ironclad beetle provide a robust and more predictable failure that could help solve these problems,” said Maryam Hosseini, who worked on this project as a PhD student.
UCI researchers built a carbon fibre composite fastener mimicking a diabolical ironclad beetle’s suture. Purdue researchers found through loading tests that the fastener is just as strong as a standard aerospace fastener, but significantly tougher.
“This work shows that we may be able to shift from using strong, brittle materials to ones that can be both strong and tough by dissipating energy as they break. That’s what nature has enabled the diabolical ironclad beetle to do,” said professor Pablo Zavattieri of Purdue University.
The research is published in the journal Nature.