Nocturnal Bull Ants Use Polarized Moonlight for Overnight Navigation

Core Concepts

Nocturnal bull ants use the polarization pattern of dim moonlight to guide their overnight navigation and homing.

Abstract

This study provides the first evidence that nocturnal bull ants (Myrmecia midas) can detect and use the polarization pattern of moonlight to navigate and home during the night. The key findings are:

Ants predictably altered their heading directions in response to experimental rotations of the ambient overhead lunar polarization pattern, indicating they can detect and use this cue for navigation.

This ability to detect and use polarized moonlight persisted across the lunar cycle, with ants responding to the pattern even under a crescent moon with only 20% lunar illumination.

Ants exhibited reduced heading shifts during waning lunar phases, when the moon's absence for part of the night leads to a gap in the available celestial cue. This suggests polarized moonlight is continuously tracked and integrated into the ants' path integrator system.

The magnitude of heading shifts in response to polarized moonlight rotations was influenced by the ants' accumulated path integration vector, with longer vectors leading to larger shifts. This aligns with how these ants use polarized sunlight during twilight navigation.

These findings indicate that nocturnal bull ants can detect and use the polarization pattern of dim moonlight as a compass cue for goal-directed navigation, integrating it into their path integrator system in a similar manner to how they use polarized sunlight during twilight periods.

Stats

The moon produces a polarized light pattern across the night sky, albeit a million times dimmer than the sun's polarized pattern.
Nocturnal bull ants (Myrmecia midas) exhibit high levels of overnight foraging activity, with up to 62.8% of the daily foraging force returning to the nest during the night.
When the ambient polarization pattern was rotated by ±45° using a linear polarization filter, ants at Nest 1 (6.0m foraging route) exhibited shift magnitudes of around 40°, while ants at Nest 2 (3.1m foraging route) exhibited shift magnitudes of around 25°.
Under a waning full moon, ants exhibited reduced shift magnitudes of around 16° compared to 40° under a waxing full moon.

Quotes

"For the first time in any animal, we show that nocturnal bull ants use the exceedingly dim polarisation pattern produced by the moon for overnight navigation."
"Nocturnal bull ants leave their nest at twilight and rely heavily on the overhead solar polarisation pattern to navigate. Yet many foragers return home overnight when the sun cannot guide them."
"We demonstrate that these bull ants use polarised moonlight to navigate home during the night, by rotating the ambient polarisation pattern above homing ants, who alter their headings in response."

Key Insights Distilled From

Polarised Moonlight Guides Nocturnal Bull Ants Home

by Freas,C. A.,... at www.biorxiv.org 12-29-2023

https://www.biorxiv.org/content/10.1101/2023.12.28.573574v2

Deeper Inquiries

How might the ants' ability to detect and use polarized moonlight vary across different nocturnal insect species, and what factors might influence this ability?

The ability of nocturnal insects to detect and use polarized moonlight can vary across different species based on several factors. Firstly, the morphology of the insects' eyes plays a crucial role in their ability to detect polarized light. Insects with specialized photoreceptors in the dorsal rim area of their eyes, like the Myrmecia ants, are more likely to detect and respond to polarized light cues. Species with less developed or sensitive eyes may not be able to utilize polarized moonlight for navigation.
Additionally, the ecological niche and foraging behavior of different nocturnal insect species can influence their reliance on polarized moonlight. Species that are more active during the night and rely on celestial cues for navigation, such as dung beetles and certain species of ants, are more likely to use polarized moonlight. In contrast, species that have different foraging strategies or habitats may not prioritize polarized light cues in their navigation.
Furthermore, the environmental conditions and the availability of other navigational cues can impact the importance of polarized moonlight. In areas with dense canopy cover or frequent cloud cover, the visibility of polarized moonlight may be reduced, affecting the insects' ability to use this cue. Species that have access to clear night skies and consistent polarized light patterns are more likely to rely on this cue for navigation.

What are the potential limitations or drawbacks of relying on polarized moonlight as a navigational cue, and how might this impact the ants' overall navigation strategies?

While polarized moonlight can serve as a reliable navigational cue for nocturnal insects like the Myrmecia ants, there are limitations and drawbacks to relying solely on this cue. One limitation is the variability in the intensity and visibility of polarized moonlight, especially during different lunar phases. For example, during crescent moon nights or when the moon is low on the horizon, the polarized light pattern may be weaker or less distinct, making it challenging for insects to detect and use this cue effectively.
Another limitation is the potential interference or obstruction of polarized moonlight by environmental factors such as clouds, canopy cover, or artificial light pollution. Insects navigating in areas with these obstacles may have difficulty relying on polarized moonlight for accurate orientation.
The reliance on polarized moonlight as a navigational cue may also be less effective in complex or changing environments where visual landmarks or other cues are more reliable. In situations where the polarized light pattern is inconsistent or overridden by other cues, insects may need to supplement their navigation strategies with additional information.
Overall, the limitations of polarized moonlight as a navigational cue can impact the ants' overall navigation strategies by introducing uncertainty or variability in their orientation and homing behaviors. To mitigate these limitations, the ants may integrate polarized moonlight cues with other navigational inputs like path integration or visual landmarks to enhance the robustness of their navigation.

Given the ants' use of both solar and lunar polarization patterns, how might their neural processing and integration of these celestial cues compare to other navigational inputs like path integration and visual landmarks?

The neural processing and integration of solar and lunar polarization patterns in the ants' navigation system are likely to involve specialized mechanisms that allow them to detect, interpret, and respond to these celestial cues. Insects like the Myrmecia ants have evolved specific photoreceptors in their eyes that are sensitive to polarized light, enabling them to perceive and differentiate between different polarized light patterns.
When comparing the processing of solar and lunar polarization cues, the ants may have distinct neural pathways or circuits dedicated to each type of cue. The detection of solar polarization patterns during twilight periods and lunar polarization patterns during the night suggests that the ants can selectively attend to and process these cues based on the time of day and the availability of light sources.
In terms of integration with other navigational inputs like path integration and visual landmarks, the ants likely have a hierarchical system that prioritizes different cues based on their reliability and relevance in different contexts. Path integration, which involves tracking the distance and direction of movement, may serve as a primary navigational strategy that is complemented by celestial cues like polarized light and visual landmarks.
The integration of multiple navigational inputs allows the ants to adapt to changing environmental conditions, variability in cue availability, and the complexity of their foraging habitats. By combining information from solar and lunar polarization patterns with path integration and visual landmarks, the ants can enhance the accuracy and robustness of their navigation strategies, ensuring successful orientation and homing behaviors in diverse and challenging environments.