Finally, the team investigated the force with which toe pads cling to surfaces.

ECONOMIST: How tree frogs keep their grip

Dr Federle and his colleagues argue that the complex arrangement of pegs and channels around the hexagonal cells has evolved to drain the mucus rapidly away from the toe pads, allowing the tree frog to grip.

ECONOMIST: How tree frogs keep their grip

They calculated the force in question from the contact area of the toe, and found that toe pads were still sticky two minutes after the sliding had stopped, long after the point when, according to their estimate of its viscosity, all the mucus would have drained away.

ECONOMIST: How tree frogs keep their grip

The photographer could only shoot Upton outside for a couple of minutes at a time before the crew, all bundled from head to toe, would rush to put heating pads in her bathing suit and cover her with electric warming coats.

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