Mechanics of jumping by slamming against water*

Semiaquatic arthropods, such as water striders and fishing spiders, can jump on water by rapidly pushing their legs against water surface. Typical-sized water striders (e.g. Aquarius remigis) adjust their leg speed not to break the water surface so that they can fully utilize the surface tension of water. However, it was recently found that large water striders (e.g. Gigantometra gigas) as well as fishing spiders break the water surface in downstroke of their middle legs, implying that water drag can also launch the small animals into the air. Here we construct a mathematical model to predict the trajectory of water jumping arthropods whether they rely on surface tension or drag of water, and compare the results with the data from high-speed visualization of those animal jumps. In particular, we pay attention to the role of air bubbles formed around superhydrophobic hairs of middle legs of large water striders that boost the water drag.