Click beetles (Elateridae) use latch-mediated spring actuation: lying on their back, the beetle slowly bends its body, storing real elastic strain energy in a hinge between the pro- and mesothorax while a peg on the prothorax presses into a socket — the latch. When the peg slips free, that stored energy converts to kinetic energy almost instantaneously, flinging the beetle into the air:
E_stored = ½ k x² (spring, loading phase)
E_stored = ½ m v² → v = x√(k/m) (energy conservation at release)
a_peak = v / τ (τ = latch release duration)
h = v²sin²θ / 2g, R = v²sin(2θ) / g (projectile arc after launch)
The stiffness k and bend distance x set how much energy the "spring" stores before release; the beetle's mass m then fixes how fast that energy can accelerate it. Because the real latch opens in roughly a millisecond, converting even a modest stored energy into velocity that fast implies enormous accelerations — measured click-beetle takeoffs reach on the order of 300–400 g, among the fastest recorded insect movements. The launch angle and computed velocity then hand off to ordinary projectile motion for the airborne arc.
- Loading phase — the hinge visibly arches as strain energy accumulates (energy bar fills).
- Release — a single near-instant frame: the peg snaps free of the socket and all stored energy leaves as kinetic energy.
- Energy check — ½kx² and ½mv² are computed independently here and shown equal, confirming the launch velocity was derived by real energy conservation, not scripted.