Locusts raised in a centrifuge have stronger skeletons.

Science Magazine gets heavy with insects that, when brought up in the “hypergravity” of a spinning centrifuge, grow stronger exoskeletons as a result:

When a person exercises regularly, their skeleton adapts to the repeated stress by becoming thicker and denser. That’s why astronauts living in low gravity and patients on bed rest can develop brittle, easily damaged bones.

But most of Earth’s animal species don’t have humanlike bones. Insects and other arthropods, which make up the vast majority of animals on Earth, instead possess a shell-like exoskeleton, which is mainly composed of a tough, flexible material called cuticle. How these exoskeletons react to the forces of gravity and other types of mechanical stress is a mystery, says Jan-Henning Dirks, a biomechanics researcher at City University of Applied Sciences Bremen.

So in the new study, Dirks and his Ph.D. student, Karen Stamm, teamed up with engineers at the Max Planck Institute for Intelligent Systems to design an unusual experiment. They built a custom centrifuge—a machine that, when spun, can exert a continuous and measurable mechanical force on whatever is inside it—complete with individually heated insect cages lit with light-emitting diodes. Inside each cage, the researchers placed a newly molted migratory locust (Locusta migratoria).

The insects are fairly easy to breed, but that’s not the only reason the scientists decided to use them for their experiment: “Locusts have got some really beautiful hind legs,” Dirks explains. Each is essentially one long slender tube, making it a breeze to calculate the mechanical forces acting upon them.

After 2 weeks, Stamm and Dirks took the locusts—now probably quite dizzy—out of the centrifuge and removed their hind legs. Next, the researchers measured how much force was required to snap them in two. The legs of locusts raised in the centrifuge were much harder to break than those from insects raised in normal gravity.

Three-dimensional x-rays of the legs revealed the source of their superstrength. The middle layer of the exoskeleton, known as the exocuticle, looked pretty much the same regardless of how the locusts were raised. The innermost cuticle layer, by contrast, looked much different: This “endocuticle” was far thicker in the centrifuge bugs, making their hind legs more resistant to breaking. “Something in the cuticle changes,” Dirks explains. “The legs become stiffer.”

As Fratzl notes, the precise origin of this change “remains to be elucidated. But the fact that both human and insect skeletons respond similarly to mechanical stress suggests the behavior may be a fundamental property of biological materials—that is, everything from plant fiber to tendon.

You can read more of the locust-leg research here, in Proceedings of the Royal Society B.