Perfectly Proportioned Legs Keep Water Striders Striding
ScienceDaily (Aug. 7, 2008) — The amazing water strider — known for its ability to walk on water — came within just a hair of sinking into evolutionary oblivion. Scientists in France and the United Kingdom are reporting that the insect’s long, flexible legs have an optimal length that keeps it afloat.
In the new study, Dominic Vella notes that scientists already know much about the water-repellant structure of the water strider’s legs and how it allows them to efficiently scoot and jump on ponds and lakes. However, the insect’s many adaptations to life on water surfaces pose scientific puzzles. Solving those mysteries may have practical applications in the design of water-walking robots that can support the maximum possible payload, they note.
Building on earlier work by scientists at Carnegie Mellon University, Vella developed a mathematical model to determine the maximum weight load that a thin, flexible cylinder — representing a water strider’s legs — can support on a liquid surface without sinking. He found that as the length of the cylinder increases, the maximum load at first increases but then reaches a plateau at some critical length.
After that length, the cylinder begins to bend and is not able to support more weight. Comparing the model to measurements on museum specimens, Vella found that the strider’s legs are typically slightly shorter than the critical length. This suggests that the water strider’s legs are just the right length: Long enough to provide maximum weight support but not long enough to bend and hinder the insect’s movement, he says.