The Science of Obama’s Fly-Swatting

A combination of good strategy and some facets of human evolution overcame the bug's impressive natural defenses.

By Allison Bond|Thursday, June 18, 2009
RELATED TAGS: EVOLUTION, INSECTS

On Tuesday, June 16, President Obama dazzled audiences during a CNBC interview by performing a difficult feat: He swatted a buzzing fly in one swift motion, leaving the creature lifeless on the carpet of the White House's East Room.

His swift blow was no small task: Flies are notoriously difficult to swat. In fact, they possess special skills that allow them to evade both flyswatters and human hands. They can place their body weight on their middle pair of feet—like all insects, they have three pairs—before they take off in flight, according to a study in Current Biology. This ability leaves them in a prime position to launch themselves in the opposite direction from where they anticipate the flyswatter will fall.

The insects are also covered with tiny hairs, called cilia, which sense even the minuscule changes in air pressure caused by a rapidly approaching hand. Additionally, their eyes have evolved to sense changes in light extremely quickly, thanks to a series of lenses that focus light and a vision system well-suited to their tiny size. That means the little buzzers quickly sense the shadow of an approaching object—such as a fly swatter—enabling them to flee before your hand can reach the table or wall. This is in sharp contrast to human eyes, which sense visual images with a single lens, allowing us to see detailed images but sacrificing some speed in our ability to see light changes.

So was Obama's swat a matter of superhuman focus and reflexes? We asked Jim Kakalios, author of The Physics of Superheroes and a physicist at the University of Minnesota. Kakalios, although duly impressed by the president's fly-killing skills, said Obama “certainly has not violated any laws of physics.” Instead, the commander-in-chief used a combination of quick reflexes and a strategic lower-arm movement to crush the insect.

Obama smacked the fly by moving his arm downward in a throwing motion, an action humans honed through evolution, Kakalios says. Our bodies consist of an intricate series of levers that make it easier to move our lower arms down than to move them up. Optimizing this throwing motion makes sense: after all, the early humans who were able to throw objects forcefully were also likely the best hunters.

In addition, the president's use of downward motion explains why he was able to move his hand so quickly: “Our arms have a built-in mechanical advantage for just that type of motion,” Kakalios says. That is, we humans bring weight towards the ground much more efficiently than we lift it up.

The final factor that sealed the fly’s fate was the way Obama strategically trapped it above his left arm. That meant the insect’s only possible escape route was flying up—straight into a descending hand.

As such, Obama used a combination of speed and strategy to crush the bug. Still, Kakalios—a superhero buff—has another theory about the president’s abilities: “Maybe Chicago tap water is very similar to Captain America’s 'Super Soldier Serum.'”

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