Geckos, tree frogs, spiders, and insects all share a special skill - they can walk up vertical surfaces and even upside down using adhesive pads on their feet. But geckos have “dry” feet, while insects have “wet” feet. Scientists have assumed that the two groups use different mechanisms to keep their feet firmly attached to a surface, but new research from David Labonte and Walter Federle, Ph.D., in the University of Cambridge's Department of Zoology provides evidence that this is not actually the case. "It has generally been assumed that the fluid on their feet must be involved in helping insects like stick insects adhere to a surface by capillary and viscous forces, in the same way that a beer glass will stick to a glass table if it's wet on the bottom," explains Labonte, lead author of the study published online on September 10, 2015 in Soft Matter, from the Royal Society of Chemistry, "but our research shows that the fluid is likely used for something else entirely; it may even help insects unstick their feet." The Soft Matter article is titled “'Rate-Dependence of 'Wet' Biological Adhesives and the Function of the Pad Secretion in Insects.” By measuring how much force was required to detach the foot of a stick insect from a glass plate at different speeds and applying the theory of fracture mechanics, Labonte and Dr. Federle found that only a “dry” contact model could explain the data. They also carried out a comparison of the sticking performance of wet and dry adhesive pads, which revealed that there is a striking lack of differences between the two, contrary to previous opinion.Insects and geckos need to walk up vertical surfaces and even upside down in order to get to the places where they feed and to escape from predators.
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