Orientation of Demagnetized Bees

The orientation of honey bee dances is affected by the earth’s magnetic field. Honey bees possess localized, well-oriented, stable and superparamagnetic domains of magnetite. Four lines of evidence suggest that the superparamagnetic domains of bees are more likely to be involved in magnetic field detectors than the stable domains. (1) Although the stable domains vary widely in size and number between bees, approximately 2× 108 superparamagnetic domains are found reliably in all bees, and are restricted to the relatively narrow size range of 300– 350 Å. This suggests that the superparamagnetic domains are more likely to have a biological function. (2) Behavioural observations of dances in null fields are difficult to reconcile with a stable-domain detector but are clearly predicted by many superparamagnetic detector models. (3) When honey bees are demagnetized, their ability to orient to the earth’s field is unaffected. This suggests that the detector either utilizes the superparamagnetic domains or depends on aligned anisotropic stable domains processed without regard to magnetic polarity. (4) Bees that have only superparamagnetic domains are able nevertheless to orient to the earth’s magnetic field, a phenomenon which indicates that permanent domains may not be required for detection.