Nocturnal ants navigate using a time-compensated lunar compass

Diurnal animals commonly navigate using a sun compass, compensating for the sun's movement to maintain accurate headings during migration or homing.^1,2,3,4,5 Because the azimuthal movement of celestial bodies accelerates during ascent and slows during descent, accurate compass navigation depends on clock-based time compensation.^3,6,7 While nocturnal animals can rely on lunar cues to guide their movement,^8,9,10,11,12 whether they can predict the highly variable arc of the moon for vector-based navigation remains unknown. Compared with the sun, the moon poses a far greater navigational challenge, as its rise time, phase, and trajectory vary dramatically across the lunar month. Here, we demonstrate that the nocturnal bull ant Myrmecia midas possesses a time-compensated lunar compass that supports their nocturnal path integrator. Nocturnal ants incorporate a generalized lunar ephemeris function, an internal prediction of the moon's arc,⁶ representing the moon's slow rise and fall via linear extrapolation combined with a rapid transition from the eastern to western sky, or speed-step,¹³ near the lunar apex. However, prediction accuracy declines around the lunar apex, where night-to-night variability in the lunar arc spreads the timing variability of individual speed-step predictions. We further show that updating the lunar compass requires occasional cross-referencing with a directionally informative skyline. Finally, these lunar predictions appear to be within-night prediction processes that are initiated when the moon is first observed. Together, these findings reveal a previously unknown form of celestial time compensation for path-integration-based navigation, demonstrating that nocturnal homing relies on a distinct predictive strategy that is adapted to the moon's variability.