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Insect Integument
Saturday, December 22, 2007
We develop a coherent view of the form and function of the integument of water-walking insects and spiders by reviewing biological work on the subject in light of recent advances in surface science. Particular attention is given to understanding the complex nature of the interaction between water-walking arthropods and the air–water surface. We begin with a discussion of the fundamental principles of surface tension and the wetting of a solid by a fluid. These basic concepts are applied to rationalize the form of various body parts of water-walking arthropods according to their function. Particular attention is given to the influence of surface roughness on water-repellency, a critical feature of water-walkers that enables them to avoid entrapment at the interface, survive the impact of raindrops and breathe if submerged. The dynamic roles of specific surface features in
thrust generation, drag reduction and anchoring on the free surface are considered. New imaging techniques that promise important insights into this class of problems are discussed. Finally, we highlight the interplay between the biology, physics and engineering communities responsible for the rapid recent advances in the biomimetic design of smart, water repellent surfaces.
SEM images of the hair layer of the water strider leg. (a) While the leg has thickness comparable to that of a human hair, it resembles a brush, whose thick carpet of hairs are tilted atB301 relative to the leg surface. Hairs are typically 30 mm long, 1–3 mm thick at the base and tapered; their density is 12 000–16 000 hairs mm 2. (b) A closer view of the hairs shows that their tips are bent inwards, towards the leg; moreover, each hair is patterned with grooves of characteristic width 400nm that run its length, (c). Note that the leg surface at the roots of the hairs, evident in (c), is patterned with isotropic roughness reminiscent of plant cuticle.
