HOW COME? An ant's hidden strength

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How can an ant lift many times its own body weight? asks reader Grace Stone.Ants seem impossibly strong. Carting boulder-sized (to them) cake crumbs across the kitchen. Carrying leaves weighing 50 times their own weight, for hundreds of feet. And not losing their grip on their massive cargo, even when walking upside down.

But before you try hoisting the nearest SUV over your head, consider this: Scientists say that when it comes to size versus strength, it's all a matter of scale. Make an ant 6 feet tall (er, long), they say, and it would actually lose its ability to lift outlandish loads. So instead of stealing a truck, a giant science-fiction ant would promptly collapse under its own weight.

How come? Make an organism larger, and its mass -- the amount of matter it contains -- increases much more than its strength. Similarly, make an organism smaller, and its strength decreases much less than its mass.

An animal expanding to five times its normal size, increasing in size by a factor of five, will weigh not five, but 125 times as much as before. That's because its volume has ballooned by 5 x 5 x 5.

When it comes to muscles, strength depends on cross-sectional area. Result? A muscle that is five times wider might be only 25 times stronger. So an ant that increased in size 100 times would actually be about a million times heavier -- but only about 10,000 times stronger. Which is why a human-sized ant couldn't stand on its own six legs, let alone lift an SUV.

But scale an animal down, and it can perform what appear to be impressive feats of strength. The average ant's body mass (a mere 1/500th ounce or so) makes its perfectly normal muscles proportionately much stronger than those of a bigger animal. Which is why ants (and many other insects) can lift or drag objects weighing five to 50 or more times their own body weight.

A 2010 study by Cambridge University researchers found that Asian weaver ants could hold objects weighing 100 times their own weight -- all while hanging upside down.

How do they do it? Surface tension between the ants' damp footpads and the surface they're walking on keeps them in place. Researchers say that when an ant is carrying a lightweight object, it folds up its feet, resulting in less contact (and less stickiness) with a surface. But when toting a heavier load, an ant will spread out its feet, creating extra surface tension. That enables the ant to safely crawl along upside down, even when a weight is tugging it toward the ground.

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