It might strike you as an office experiment devised in boredom: piling up staples and seeing how long it takes for them to collapse. But the researchers behind the investigation are serious, and they think it could help explain how "entangled ensembles" benefit the animal kingdom. The team created a mound of staples by pouring them into a cylinder roughly the size of an espresso mug. After removing the cylinder, they subjected the staples to fast, 30-Hertz vibrations on a device technically known as a shaker and measured how long it took for the mound to collapse. They then repeated the experiment for staples of the same width but different leg sizes. Staples with a length-to-width ratio of about 0.4—that's a bit stubbier than your typical office staple—stayed piled up the longest, the team reports in Physical Review Letters. This ratio appears to balance the number of entanglements—interlocked legs, that is—that staples have with their neighbors with the staple density, both of which make the mounds more stable. The results suggest that the limbs and jaws of species such as the fire ant (Solenopsis invicta, inset), which interlock to create floating bridges and shelters, also exploit optimal length-to-width ratios.
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This article has been updated 29 May to give the genus and species of the fire ant pictured: Solenopsis invicta.