Page 100 - Engineering in Nature

Engineering in Nature

The answer is linked to the cleft-shaped sensors on its eight feet,
which are so sensitive that they can detect vibrations smaller than one
millionth of a millimeter.
Let us imagine that a butterfly lands somewhere near a scorpion,

setting up two types of vibrational waves in the ground. The first type
are so-called volume waves and move faster than 150 meters a second
(492 feet/second). The second, known as Rayleigh waves, travel par-
allel to the surface at more than 50 meters a second (164 feet/second).
The scorpion determines the distance to its prey by analyzing the dif-
ference between the times at which the two waves arrive. 30
Of course, knowing the prey's distance still doesn't establish its
exact location. The scorpion must also determine the prey's direction.
The scorpion's legs stand on the ground in a circle approximately 5
cm in diameter. That makes for a difference as small as 5 milliseconds
(1/200th of a second) between the arrival of the Rayleigh wave from

For millions of years, the desert scorpion has been able to detect the slightest vibra-
tion on the surface of the sand. Human beings have been able to make vibration de-
tectors only after long years of accumulated knowledge.

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