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bioRxiv · 10.1101/2025.08.28.672594

Nocturnal Navigation via a Time-Compensated Lunar Compass in Bull Ants

Freas, C. A.·Cheng, K.
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Abstract

Diurnal navigators are well known to orient via the sun, compensating for its movement over time by linking solar position and speed with terrestrial reference points (Beetz & el Jundi, 2018; Dingle, 2014; Dyer, 1987; Mouritsen & Frost, 2002; Stalleicken et al., 2005; Wehner & Lanfranconi, 1981; Wehner & Muller, 1993). In contrast to the sun, the moon is not only dimmer, but its presence is also highly variable, both temporally and in its illuminance, making it a more complex cue to predict. Yet nocturnal animals employ a celestial compass to orient at night (i.e. the moon and stars; (Dacke et al., 2003, 2013; Dreyer et al., 2025), but navigation via a time-compensated lunar compass has yet to be demonstrated. Nocturnal bull ants (Myrmecia midas) navigate home overnight under the dimmest of visual conditions, relying in part on a nocturnal path-integration system informed by lunar cues (Freas et al., 2024). Here, we show the first evidence of a time-compensated lunar compass in a homing animal, with path-integrating ants adjusting path headings by predicting the lunar azimuthal position throughout the night. Ants predict the moons future position based upon a generalised internal estimate of the lunar ephemeris. Rather than detailed knowledge of the moons nightly schedule, these ants form a lunar path representation via a speed-step function, reflecting the moons accelerating then decelerating arc. However, these ants also predictably under- or overestimate the shape of this arc based on individual experience, suggesting a level of temporal uncertainty regarding when the moon rapidly shifts from the eastern to western sky. Additionally, updating this lunar compass relies on the presence of a directionally informative skyline, which allows occasional cross-referencing of lunar movement with external fixed compass cues near the horizon.

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Freas, C. A., Cheng, K.. 2025-09-01. Nocturnal Navigation via a Time-Compensated Lunar Compass in Bull Ants. https://doi.org/10.1101/2025.08.28.672594

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