Horticulturalists have a love–hate relationship with flea beetles. While some species keep weeds in check, others are pests with a voracious appetite for the crops we cultivate. And these diminutive pests have another claim to fame: they perform spectacular leaps to evade predators when startled. Konstantin Nadein and Oliver Betz from the University of Tübingen, Germany, explain that the insects have fascinated scientists since the 1920s: ‘Nevertheless … the exact mechanism of energy storage and release in [jumping] flea beetles is still not fully understood’, they say. Intrigued by the tiny beetles’ agility, Nadein and Betz filmed the antics of seven members of the flea beetle family and scrutinised their anatomy to pin down the fine details of the feat.
Filming the explosive leaps at 2000 and 3000 frames s−1, the duo could see the beetles taking off in less than 2.25 ms, reaching g-forces of up to 340 and hitting top speeds of 3.6 m s–1 (the equivalent of a human jumping at almost 2.5 km s−1) as they pinged themselves into the air. Also, when the pair used high-powered scanning electron microscopy, X-rays and fluorescence microscopy to look at the structures inside the beetles’ legs, they saw a specialised stretchy tendon linking the femur and tibia that can store an enormous amount of energy, which is released instantaneously when the flexor muscles – holding the tibia in place during the preparation phase of the jump – suddenly relax. Nadein and Betz say, ‘The calculated specific joint power (max. 0.714 W g−1) of the femoro-tibial joint during the jumping movement and the fast full extension of the hind tibia (1–3 ms) suggest that jumping is performed via a catapult mechanism’.