Small but Mighty: The Hidden Mechanisms that Power Insect Bodies

Written by: El Hebert '24
Edited by: Ashley Nee '22

It’s hard to be an arthropod. They live fast, dangerous lives, and to strike, evade, or communicate, they need to transcend the limits of their small bodies. Yet, all around us, they defy those limits spectacularly.

Fleas leap in the blink of an eye. Mantis shrimp punch with the force of a bullet. The tiny planthopper, vibrating to send signals through the soil, outputs ten times more power than its abdominal muscles should be able to produce [1]. How do they do it?

Biomechanical studies on these high-energy movements have revealed that small animals rely on elastic-recoil mechanisms, which load energy slowly and release it all at once. In other words, they have latches and springs, or strung bows, built into their bodies [2]. 

Whenever you snap your fingers, you take advantage of the same principles. You “load” energy into the tendons that control the hand, “latching” the system with the friction between your thumb and finger. When the latch finally slips, your finger smacks into your palm hard enough to produce a loud click. 

This is the same mechanism that some ants use to snap their two jaws shut: they press their mandibles together, then let them rapidly slip past each other. Other species across the ant family go about things in the opposite way, latching and releasing their mandibles from the open position, but the “snap-jawed” dracula ants bite fastest of all, at 90 meters per second [3].

Some bugs have their latches and springs on the inside, like the pesky, catapult-propelled flea. This impressive little nuisance locks the “knee” joints in its hindlegs and then tenses muscles that squeeze its stiff exoskeleton, storing energy there. The bounce-back when the joints unlock forces the flea’s legs to extend, which flings the whole animal into the air [4]. 

Though weak on their own, those cleverly rigged legs allow fleas to jump 50 times their body length, easily dodging predators, or hopping to a new animal host [5]. Froghoppers, larger insects that beat the flea in relative jumping height and speed, use a similar mechanism [2].

The common cat flea and its catapult legs. Its bent “knees” (the trochanter joints) lock in place to prime for a jump. Katja ZSM, Wikimedia Commons.

These efficient power-amplified systems hold plenty of promise for human engineers, too. One research team at the University of Massachusetts, Amherst, built an experimental robot (dubbed Ninjabot) that attempted to replicate the recoil mechanism in the mantis shrimp’s fast-striking arms. In measured speed, it tied with some of the slower shrimp - but, being made of steel, it weighed nine kilograms [6]. Clearly, composition is just as important as construction for the arthropods and their imitators.

Chemists have already identified the “super elastic rubber” protein, resilin, that fleas and froghoppers use to reinforce their springs. It can stretch to over three times its original length without breaking, and its structure may inform the development of new materials [7]. In the mantis shrimp, on the other hand, minerals fortify the exoskeleton, just like a man-made metal spring [2]. 

Another study, focusing on the jumping click beetle, offers a clue as to how the stiffer parts of the mechanism avoid long-term damage - instead of relying on dry friction between each other to slow down, these components are smooth, and shaped to take advantage of air braking [8]. 

The protruding peg on the underside of this click beetle’s thorax fits into a slot in the abdomen as part of its “click” mechanism. Katja Schulz, Wikimedia Commons.

This research reminds us that important new discoveries often come from the most unlikely sources. As it turns out, even parasitic insects contain perfected machinery. 

For our part, we’re a long way from recreating what evolution has devised over millions of years. But with insights from the study of snapping ants, punching shrimp, and jumping fleas, we humans can work to make our own leaps, too.

​Works Cited:

[1] Davranoglou LR, Cicirello A, Taylor GK, Mortimer B. Planthopper bugs use a fast, cyclic elastic recoil mechanism for effective vibrational communication at small body size. PLoS biology [Internet]. 2019 [Cited 2021 Feb. 27]; 17(3). DOI: https://doi.org/10.1371/journal.pbio.3000155

[2] Patek SN, Dudek DM, Rosario MV. From bouncy legs to poisoned arrows: elastic movements in invertebrates. Journal of Experimental Biology [Internet]. 2011 [Cited 2021 Feb. 27] 214(12),1973-80. DOI: https://doi.org/10.1242/jeb.038596.

[3] Larabee FJ, Smith AA, Suarez AV. Snap-jaw morphology is specialized for high-speed power amplification in the Dracula ant, Mystrium camillae. Royal Society open science [Internet]. 2018 [Cited 2021 Feb. 21]; 5(12). DOI: https://doi.org/10.1098/rsos.181447.

[4] Sutton GP, Burrows M. Biomechanics of jumping in the flea. Journal of Experimental Biology [Internet]. 2011 [Cited 2021 Feb. 21]; 214(5), 836-47. DOI: https://doi.org/10.1242/jeb.052399.

[5] Cassidy J. A Flea's Fantastic Jump Takes More Than Muscle. KQED Deep Look [Internet]. 2020 [Cited 2021 Feb. 21]. Available from: https://www.kqed.org/science/1957872/a-fleas-fantastic-jump-takes-more-than-muscle.

[6] Zyga L. Ninjabot strikes with force of a mantis shrimp. Phys.org [Internet]. 2014 [Cited 2021 Feb. 21]. Available from: https://phys.org/news/2014-02-ninjabot-mantis-shrimp.html.

[7] Qin G, Hu X, Cebe P, Kaplan DL. Mechanism of resilin elasticity. Nature communications [Internet]. 2012 [Cited 2021 Feb. 21]; 3(1), 1-9. DOI: https://doi.org/10.1038/ncomms2004.

[8] Bolmin O, Socha JJ, Alleyne M, Dunn AC, Fezzaa K, Wissa AA. Nonlinear elasticity and damping govern ultrafast dynamics in click beetles. Proceedings of the National Academy of Sciences [Internet]. 2021 [Cited 2021 Feb. 21]; 118(5). DOI: https://doi.org/10.1073/pnas.2014569118.