Spiders probably use polarised light as a compass when they return home after foraging. Marie Dacke of the University of Lund in Sweden studied the spider Drassodes cupreus and found that two of its eight eyes have built-in filters that allow them to detect the polarisation of light. The animals managed to find their way back to their nests under polarised light in the laboratory. Under unpolarised light, however, it was no better than random navigation. Dacke believes that the eyes of other spiders may share the same ability ( Nature , Vol 401 p470).
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