Biomagnetism: An Orientation Mechanism in Migrating Insects?

The ability of short lived insects to migrate seasonally over long distances requires the use of some heritable, direction-finding mechanism. Biologically synthesized magnetic particles, functioning like a built-in compass, may serve as one such mechanism by enabling orientation in the earth's magnetic field. Biomagnetism has been a leading candidate to explain geomagnetic orientation in animals. Except for 2 species, insects have not been examined for evidence of magnetic particles. In this study 9 insect species were tested. Five migratory (moths and butterflies) and 4 non-migratory (crickets) species were compared to reveal any correlation between the presence of magnetic particles and migratory behavior. Only 1 migrant, the monarch butterfly (Danaus plexippus L.), displayed evidence of biomagnetism. All non-migrants possessed significant levels of magnetism, the function of which if any, is not known.