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Inside JEB |
SPIDERS GET ATTACHED
kathryn{at}biologists.com
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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?
References
Kesel, A. B., Martin, A. and Seidl, T. (2003).
Adhesion measurements on the attachment devices of the jumping spider
Evarcha arcuata. J. Exp. Biol.
206,2733
-2738.
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