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Polarized moonlight orientates bugs

11 Jul 2003

Dung beetles use the polarization of moonlight to move in a straight line.

The African dung beetle uses polarized moonlight to roll its food in a straight line, according to researchers in Sweden and South Africa. The team says this is the first discovery of an animal that uses the Moon’s polarization pattern as a nocturnal compass, but believes that other animals may turn out to have this ability (Nature 424 33).

Marie Dacke from the University of Lund in Sweden and her colleagues from the universities of the Witwatersrand and Pretoria in South Africa say that many creatures use the natural polarization of the Sun as a means of orientation. “The Scarabaeus zambesianus is the first animal known to use the million-times dimmer polarization of moonlight for the purpose,” her team reports.

Dacke’s team performed two experiments. Firstly, they tracked the movements of the beetles under various night-skies. The team observed that the beetles only followed a straight path on moonlit nights. If the Moon was obscured, the beetles went on a random walk.

The second experiment showed that the creatures used the polarization of the moonlight instead of the Moon’s position as a guide.

To do this, Dacke and colleagues placed a polarization filter over the beetle and shaded the Moon from its field-of-view. “The Moon’s polarized light pattern appeared to turn through 90° as the beetles continued to roll [their dung-ball] beneath the filter,” report the authors. “In response to this light rotation, the beetles turned close to the expected 90°, either left or right.”

Moving away from a dung pile in a straight line is the best way for a dung beetle to keep its food. Although this is the first discovery of a creature with a nocturnal compass, the team believes other animals may posses this effective characteristic.

Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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