Did you know that there is a species of beetles with a shell so strong that you could run it over with your car, and you still wouldn’t be able to crush it? However, until recently, scientists had no idea why they were so tough. It turns out that these beetle’s outer wing cases, or elytra, are made up of interlocking pieces in a “jigsaw”” design pattern and this greatly increases the strength of the exoskeleton.

The beetle is called the ironclad beetle, or Phloeodes diabolicus, and it measures around 0.6 to 1 inch in length. They are found in woodlands across western North America, and they will usually live under the bark of trees. Scientists believe that the ancestors of these insects could fly, but the ironclad beetles have lost this ability a long time ago due to their elytra fusing together.

Entomologists are perhaps the most familiar with the strength of this beetle’s shell. Many times, in their efforts to store, display or mount one of these specimens, entomologists will end up with an intact shell and a bunch of bent steel pins.

Some researchers have performed a series of compression tests in order to find out the amount of force that the shells could withstand without cracking. The result was 149 newtons or 33 lbs. of continuous force, which is twice as much as other beetle species and 39,000 times its own body weight.

A cross-section of the exoskeleton was examined under the microscope in order to understand where this strength comes from. The analysis showed that the elytra had lateral support structures to distribute the weight more evenly across the beetle’s back, and that the elytra were fused together at the seam for further reinforcement.

In beetles that have the ability to fly, the elytra are notched together in a tongue-and-groove design, that allows them to open and close smoothly, while providing a degree of structural strength. In the ironclad beetle however, the elytra are fused in a jigsaw puzzle pattern, preventing them from opening and offering extra strength. The pieces of the elytra that create this jigsaw pattern are called blades and they also help distribute strength across the shell.

When trying to find the optimal structure while 3D printing samples of this jigsaw pattern, researchers found that sutures with five blades could bear the heaviest loads. Upon further research of the blades themselves, the researchers found microstructures layered on top of each other which further diverted stress from the more vulnerable parts of the joint. The vulnerabilities of the narrow necks within the pattern were protected by these microstructures and helped lock the shell in place even more securely.

Through this research, scientists could unlock new architectural patterns that can be used to make buildings stronger and more resistant to physical tensions. In fact, these designs have already shown a considerable increase in toughness when compared to commonly used engineering joints.