Cataglyphis ants have a polarity-sensitive magnetic compass

Spatial orientation based on the geomagnetic field (GMF) is a widespread phenomenon in the animal kingdom, predominantly observed in long-distance migrating birds,¹ sea turtles,² lobsters,³ and Lepidoptera.^4,5 Although magnetoreception has been studied intensively, the mechanism remains elusive. A crucial question for a mechanistic understanding of magnetoreception is whether animals rely on inclination or polarity-based magnetic information. Inclination-based magnetic orientation utilizes the angle between the magnetic field lines and gravity, indicating poleward and equatorward. In contrast, polarity-based magnetic orientation allows animals to detect the polarity of the GMF, the north and south direction of the field vector. Cataglyphis desert ants are excellent experimental models for testing whether magnetic inclination or polarity of the magnetic field is used for navigation. Desert ants are solitary foragers with exceptional navigational skills.⁶ When the ants leave their underground nest for the first time to become foragers, they perform learning walks for up to three days to learn the visual panorama and calibrate their compass systems.^7,8 The ants repeatedly stop their forward movement during learning walks for performing turns (pirouettes), interrupted by stopping phases. Gaze directions during the longest stopping phases are directed toward the nest entrance.⁹ We experimentally manipulated look-back behavior systematically by altering polarity or inclination of the GMF. We demonstrate that Cataglyphis ants, contrary to most other insects studied,¹⁰ possess a polarity-sensitive magnetic compass, making them ideal experimental models for narrowing down the evidence for particle-based mechanisms underlying magnetosensation in this insect.