Certain animals, including some birds and fish, are guided by magnetic fields, and researchers have isolated magnetic cells that could be at the root of this internal compass.

Michael Winklhofer at Ludwig-Maximilians-University in Munich, Germany, and his colleagues took epithelial cells from the rainbow trout nose and exposed them under a microscope to a moderately strong, rotating magnetic field. A few of the cells spun at the same frequency as the magnetic field, indicating that they were sensitive to the field, whereas the other cells did not alter their behaviour. High-resolution imaging showed that the responsive cells had micrometre-scale structures composed of iron-rich crystals attached to their cell membranes. These caused the cells to align with the magnetic field.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1205653109 (2012)