What goes up must come down: biomechanical impact analysis of falling locusts

Abstract

Many insects are able to precisely control their jumping movements. Once in the air, the properties of the actual landing site, however, are almost impossible to predict. Falling insects thus have to cope with the situation at impact. In particular, for insects jumping to escape predators, a controlled landing movement appears to be a major evolutionary advantage. A quick recovery into an upright and stable body posture minimizes the time to prepare for the next escape jump. In this study, we used high-speed recordings to investigate the falling and in particular the impact behavior of Schistocerca gregaria locusts, a common model organism for studies on the biomechanics of jumping. Detailed impact analyses of free-falling locusts show that most insects typically crashed onto the substrate. Although free-falling locusts tended to spread their legs, they mostly fell onto the head and thorax first. The presence of wings did not significantly reduce impact speed; however, it did affect the orientation of the body at impact and significantly reduced the time to recover. Our results also show that alive warm locusts fell significantly faster than inactive or dead locusts. This indicates a possible tradeoff between active control versus reduced speed. Interestingly, alive insects also tended to perform a characteristic bending movement of the body at impact. This biomechanical adaptation might reduce the rebound and shorten the time to recover. The adhesive pads also play an important role in reducing the time to recover by allowing the insect to anchor itself to the substrate.