Pendulum-based measurements reveal impact dynamics at the scale of a trap-jaw ant

Abstract

Small organisms can produce powerful, sub-millisecond impacts by moving tiny structures at high accelerations. We developed and validated a pendulum device to measure the impact energetics of microgram-sized trap-jaw ant mandibles accelerated against targets at 105 m s−2. Trap-jaw ants (Odontomachus brunneus; 19 individuals; 212 strikes) were suspended on one pendulum and struck swappable targets that were either attached to an opposing pendulum or fixed in place. Mean post-impact kinetic energy (energy from strike converted to pendulum motion) was higher with a stiff target (21.0-21.5 µJ) than a compliant target (6.4-6.5 µJ). Target mobility had relatively little influence on energy transfer. Mean contact duration of strikes against stiff targets was shorter (3.9-4.5 ms) than against compliant targets (6.2-7.9 ms). Shorter contact duration was correlated with higher post-impact kinetic energy. These findings contextualize and provide an energetic explanation for the diverse, natural uses of trap-jaw ant strikes such as impaling prey, launching away threats, and performing mandible-powered jumps. The strong effect of target material on energetic exchange suggests material interactions as an avenue for tuning performance of small, high acceleration impacts. Our device offers a foundation for novel research into the ecomechanics and evolution of tiny biological impacts and their application in synthetic systems.

Latch-mediated spring actuation (LaMSA): the power of integrated biomechanical systems

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Behavior and morphology combine to influence energy dissipation in mantis shrimp (Stomatopoda)

“…For instance, trap-jaw ants close their jaws at ultrafast speeds, using these impacts for multiple purposes, from capturing soft-bodied prey to escaping predation by propelling themselves off hard substrates ( Spagna et al, 2009 ). By studying the kinematics of trap-jaw ant impacts, Jorge et al (2021) found that jaw closure transferred more energy to stiff targets than to compliant ones, showing how the same impact, delivered to different materials, can achieve different biological tasks.…”

Combining behavior and mechanics approaches reveals the dynamics of animal impacts in mantis shrimp (Stomatopoda)

“…For instance, trap-jaw ants close their jaws at ultrafast speeds, using these impacts for multiple purposes, from capturing soft-bodied prey to escaping predation by propelling themselves off the hard substrate (Spagna et al, 2009). By studying the kinematics of trap-jaw ant impacts, (Jorge et al, 2021) found that jaw closure transferred more energy to stiff targets than compliant ones, showing how the same impact, delivered to different materials, can achieve different biological tasks.…”