Scampering up rough surfaces is fairly straightforward if you can get a grip, but staying attached to smooth surfaces is much trickier. Some creatures ooze a sticky goo from pads on their feet to adhere themselves to walls and ceilings. Other animals have opted for a drier approach; they have hundreds of thousands of microscopic hair-like structures that bond them to vertical surfaces. Antonia Kesel wondered how these tiny hair-like setules attach an animal to a smooth surface, so she began probing jumping spider's feet to find the origin of their super-adhesion(p. 2733).
Working with her team, she measured the setule's size by electron microscopy, and found that each settule is flattened at one end, to produce a tiny pad. As each jumping spider has well over half a million tiny hairs on its feet, the area soon adds up, but even, so each arachnid only has a microscopic footprint. So how do the miniscule pads attach the spider to a wall? The group probed individual setules with an atomic force microscope, and measured the force necessary to pull the probe away from a setule; almost 40 nN, which adds up to enough sticking power to support an animal that weighs over 2 g. Kesel's spiders only weigh a tiny fraction of that, so the setule's adhesive force anchors them very securely to any surface they choose. Which then poses another question; how arthropods ever pry their feet free, once attached?