The effect of natural substrates on jump height in click-beetles

Inverted click-beetles (Elateridae) jump to right themselves, providing enough energy to launch the body many body lengths into the air. We tested whether the apparently redundant jump energy could be an adaptation for jumping from compliant surfaces that absorb energy, in the natural habitat. Jump height was measured in beetles jumping from natural substrates and from an apparatus we designed, allowing them to adjust the level of jump energy attenuated by the substrate. Jump height was dramatically reduced (by c. 75%) when jumping from leaves that covered approximately half of the study site. In the remaining area, jumping for righting was either not required or not substantially attenuated. Therefore, the available power for jumping results in low jumps that are barely sufficient for righting when jumping from compliant surfaces covering c. 50% of the natural habitat. The decrease in jump height was correlated with the amount of work absorbed by the substrate. We therefore conclude that the beetles do not adjust the muscle work invested in jumping to adjust for changes in substrate stiffness. Scaling considerations of the jumping mechanics suggest that substrate compliance becomes a bigger problem for larger beetles. 6.The effect of substrate compliance needs to be taken into account while addressing the functional ecology of jumping animals.