Why It's So Hard to Swat a Fly

PASADENA, Calif. - Anyone who has ever missed a fly with a swatter already knows the outcome. Now researchers using high-speed cameras have explained why: the fly spots the threat, calculates an escape route and repositions its legs — all in about 100 milliseconds.

The Caltech team found that within a fifth of a second of seeing something loom, a fruit fly moves its middle legs into position, adjusts its body posture and leaps away — always aiming roughly opposite to the threat.

"The fly isn't just jumping blindly. It's doing vector math with a brain the size of a poppy seed," said the study's lead author.

The researchers' practical advice for frustrated humans: don't aim at the fly. Aim slightly ahead of it, because the fly will jump forward and up. Come in slowly — the fly's threat response triggers on fast movement.

The work, published in a biology journal, has applications beyond the kitchen: engineers study the fly's reflexes to design obstacle-avoiding robots and, someday, driverless vehicles.

Flies have outwitted swatters for at least 65 million years. Science has now confirmed it was never a fair fight.

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