Conquering the slippery slope, described in Nature, vol. 437, p733, 29 Sep 2005. Many small insects can walk on water because of the surface tension of the water, but the same surface tension creates a problem for very small insects when they walk to the edge of the water and want to get off. At the edge, the surface of the water slopes up. This is called the meniscus, and can be seen around the edge of the water surface of a glass of water. For a millimetre sized insect it forms a huge slippery slope they cannot walk up.

David Hu and John Bush of the Massachusetts institute of Technology worked out how small insects and larvae are able to escape from the water. By bending their bodies and not moving their legs they are able to deform the water surface so that capillary action propels them up the slope. Hu and Bush write: “The ability to climb menisci is a skill exploited by water walking insects as they seek land in order to lay eggs or avoid predators; moreover it was a necessary adaptation for their ancestors as they evolved from terrestrials to live exclusively on the water surface.”

Editorial Comment: The ability to walk on water requires special design features that can only be simulated by creative intelligence. The study described above shows that walking off water also requires clever design. Unless the first insect to walk on water was also programmed with the ability to move its body in the right way to get off the water, we agree that it is hard to see how water walking insects could have “evolved from terrestrials to live exclusively on the water surface.” It makes far more sense to believe that water walking insects were pre-programmed to make the correct body movements for both walking on the water as well as changing their movements when they arrived at the water’s edge. (Ref. locomotion, design, insects)


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