A process called magnetoreception enables numerous species of organisms of the animal kingdom, including arthopods and vertebrates, to use Earth’s magnetic field for their survival-dependent physiological ability to orient themselves and navigate in their ecological niche, functional abilities that begin with perception of the direction and/or intensity of the magnetic field locally passing through them.  
Few subjects in animal behavior have more exotic mystery than magnetic-field sensitivity. A force we cannot sense, generated by events no one completely understands, creates field lines that pass through our bodies without any evident effect on us or on them. It is an energy felt as much by migrating lobsters on the sea floor as by ocean-crossing birds thousands of meters overhead, transduced in generally poorly understood ways....But for many animals, the reliance is far older and more basic: their life-or-death ability to find their way around in the world depends on correctly interpreting the earth's magnetic field.
- Wiltschko R, Wiltschko W. (2012) Magnetoreception. Chapter 8, pp. 126-141. In: Sensing in Nature, Advances in Experimental Medicine and Biology, Volume 739.
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