J. Exp. Biol. 212, 3473–3477 (2009)

Many animals can sense Earth's magnetic field, but for some species, it remains uncertain whether this ability depends on embedded magnetic particles or magnetically sensitive 'radical pair' chemical reactions of light-sensitive molecules.

Martin Vácha and his colleagues at Masaryk University in the Czech Republic exposed American cockroaches to a magnetic field in which the position of magnetic north changed by 60° every 5 minutes. This normally makes cockroaches restless. The team also applied a radio-frequency field at only a fraction of Earth's field intensity to jam the creature's magnetic sensing system. At a certain frequency, the cockroaches stayed calm. Other radio frequencies had the same effect, but at higher field strengths.

Because the radio-frequency field should not affect a magnetic-particle-based sensor, the result suggests that insects use a radical-pair-based method of sensing magnetic fields.