You can't squish this 'iron' beetle. Now, scientists know why. - Live Science

Diabolical ironclad beetles are almost unbreakable — you can smack them, stomp on them or run them over with a car, and they'll scamper away uncrushed.

Now, scientists know why these beetles' outer wing cases, known as elytra, are so tough — they're made up of a series of smoothly interlocking puzzle parts; the geometry and internal structure of this "jigsaw" design increase the strength of the beetle's armor. .

Though their ancestors could fly, ironclad beetles lost their flight capabilities long ago, and their elytra are fused together, forming a crush-resistant shield. .

Microscopic analysis of exoskeleton cross-sections showed lateral support structures that made some parts of the elytra stiffer than others, to distribute weight uniformly over the beetle's back and protect its organs.

And further reinforcement came from the seam where the elytra fused together. .

But in ironclad beetles, the fused elytra fit together like pieces in a jigsaw puzzle along the length of the insect's abdomen.

The protruding parts of these interlocking pieces, called blades, also distribute stress across the exoskeleton, preventing it from cracking.

The scientists also detected layered microstructures in cross-sections of the blades that further diverted stresses away from the most vulnerable parts, protecting the narrow "necks" of the interlocking puzzle pieces from fractures and actually causing the pieces to lock together more securely.