L. Brian Stauffer
Aimy Wissa, Marianne Alleyne and Ophelia Bolmin

Oh Snap! How Click Beetles Use A Basic Principle of Mechanical Engineering

Jan. 19, 2021
Researchers explain the inner workings of a click beetle’s defensive snapping sound. Hint: Think popper toys.

University of Illinois researchers can now explain the physical mechanisms behind click beetles’ clicking maneuver.

Belonging to the Elateroidea family, a click beetle (or snapping beetle) is characterized by its signature click mechanism. A click beetle can propel itself more than 20 body lengths into the air using a unique hinge-like tool in their thorax, just behind the head, to jump.

A spine on its prosternum can be snapped into a corresponding notch (peg) on its mesosternum that can unhinge and launch the beetle into the air. The clicking or snapping sound is a defense mechanism to avoid predation, and is useful when the beetle is on its back and needs to get back on its feet.

Although the jump’s motion has been written about extensively, the physical mechanisms that enable the maneuver have not. A multidisciplinary study, led by University of Illinois Urbana-Champaign mechanical science and engineering professors Aimy Wissa and Alison Dunn, entomology professor Marianne Alleyne, and mechanical science and engineering graduate student and lead author Ophelia Bolmin examined the forces behind this super-fast energy release.

Their study, published in the Proceedings of that National Academy of Science, looks at the flow of energy between muscle, hard and soft cuticle and the body structures.

In the video (see below), Dunn explained their research explored two questions: 1. How is energy stored and released through the body to produce the powerful jump without using its legs? 2. What specific anatomy contributes to the energy flow, the quick bending or clicking maneuver?

How the Hinge Works

To determine how the hinge works, the team used high-speed X-rays to observe and quantify how a click beetle’s body parts move before, during and after the ultrafast energy release.

“The hinge mechanism has a peg on one side that stays latched onto a lip on the other side of the hinge,” Alleyne said. "When the latch is released, there is an audible clicking sound and a quick unbending motion that causes the beetle’s jump.”

The ultrafast motion can be seen using a visible-light camera and helped the researchers understand what occurs outside the beetle. And to understand how the beetle’s internal anatomy controls the flow of energy between the muscle, other soft structures and the rigid exoskeleton, the researchers used X-ray video recordings and an analytical tool called system identification. 

When the research team modeled the clicking motion forces and phases, they observed large-yet-relatively-slow deformations in the soft tissue part of the beetle’s hinge in the lead-up to the fast, unbending movement.

“When the peg in the hinge slips over the lip, the deformation in the soft tissue is released extremely quickly, and the peg oscillates back and forth in the cavity below the lip before coming to a stop,” Wissa said. “The fast deformation release and repeated, yet decreasing, oscillations showcase two basic engineering principles called elastic recoil and damping.”

The acceleration of this motion is more the 300 times that of the Earth’s gravitational acceleration, noted the researchers. “Surprisingly, the beetle can repeat this clicking maneuver without sustaining any significant physical damage,” Dunn said. “That pushed us to focus on figuring out what the beetles use for energy storage, release and dissipation.”

Bolmin said the beetle uses a phenomenon called snap-buckling to release elastic energy extremely quickly. This basic principle of mechanical engineering is the same principle that you find in jumping popper toys, she explained.

“We were surprised to find that the beetles use these basic engineering principles,” said Wissa. “If an engineer wanted to build a device that jumps like a click beetle, they would likely design it the same way nature did.

Engineering Meets Biology

The beetle study provides guidelines for studying extreme motion, energy storage and energy release in other small animals, such as trap-jaw ants and mantis shrimps. The researchers consider this work to be a great example of how engineering can learn from nature and how nature demonstrates physics and engineering principles.

“These results are fascinating from an engineering perspective, and for biologists, this work gives us a new perspective on how and why click beetles evolved this way,” Alleyne said. “This kind of insight may have never come to light, if not for this interdisciplinary collaboration between engineering and biology. It opens a new door for both fields.”

Access the Study

Ophelia Bolmin et al., “Nonlinear elasticity and damping govern ultrafast dynamics in click beetles,” PNAS (2020).

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