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 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 head and thorax first. The presence of wings did not significantly reduce impact speed, however affected 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 vs. 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 to reduce the time to recover by allowing the insects to anchor itself to the substrate.