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Bull ants use moonlight for nighttime navigation

A new study published in the journal eLife has found that nocturnal bull ants use low-level moonlight to navigate at night. 

The research, highlighted by the editors for its significant contribution to understanding nocturnal navigation and the use of polarized light by animals, has shown that bull ants can detect polarized moonlight patterns, similar to how they utilize solar polarization during the day. 

This discovery adds a new dimension to our knowledge of animal sensory ecology and navigation strategies.

Photoreceptors for animal navigation 

Many animals navigate by using the position of the sun or moon, but they often rely on detecting patterns of polarized skylight when these celestial bodies are obscured. 

These patterns, known as e-vectors, are produced when light passes through the upper atmosphere. 

Specialized photoreceptors in the eyes of these animals detect the light cues and combine this information with terrestrial cues to adapt their navigation strategy, known as their path integrator.

“Like solar polarization, though a million times weaker, the moon reflects sunlight and produces a polarized moonlight pattern determined by its position in the sky,” explained lead author Cody Freas, a research fellow at Macquarie University in Australia.

Studying nocturnal bull ants 

The scientists studied two nests of nocturnal bull ants (Myrmecia midas) on the Macquarie University Wallumattagal campus in Sydney, over seven months. 

Bull ants typically begin foraging within 20 minutes of sunset, traveling from their nests to nearby eucalyptus trees and returning either overnight or during morning twilight. 

The researchers tested the ants across various lunar cycles, using filters to alter the direction of polarized moonlight. They recorded the ants’ movements to understand their navigational responses.

Bull ant navigation by polarized moonlight

Bull ants altered their direction predictably in response to changes in lunar light polarization, indicating they can detect and use these patterns for navigation.

This behavior was consistent throughout the lunar cycle, demonstrating that polarized moonlight serves as a stable cue for the ants’ path integration.

The experts also observed that foragers reduced their directional changes when the moon was waning, suggesting that the absence of the moon for part of the night creates a gap in navigational cues. This indicates that ants continuously track moonlight polarization, similar to how they track solar polarization.

“This is the first evidence of foraging ants using polarized moonlight to navigate to a goal location,” said senior author Ken Cheng, a professor of animal behavior at Macquarie 

“Our findings suggest that polarized moonlight is detected and integrated into the ant’s path integrator along the same visual pathways as polarized sunlight, and that these animals can weight the information provided, thus tailoring their navigational decisions to closely match the reliability of available navigational information.”

Solar and lunar polarization

Freas noted that this represents a navigational system that can use the same underlying neural circuitry to navigate at both day and night with no mechanistic alterations, switching between solar and lunar polarization for compass cues. 

“Thus, a polarization pattern-based sky compass becomes a useful ‘all hours’ directional compass with only visual light sensitivity needed to make solar navigation-based tools work at night.”

More about bull ants

Bull ants are a genus of large, aggressive ants native to Australia. They are known for their powerful stings, which can cause intense pain and, in some cases, allergic reactions. 

These ants vary in size, with some species reaching up to 40 millimeters in length. Bull ants have excellent vision, capable of tracking and following intruders from a distance of one meter or more. 

Bull ants are solitary hunters, foraging individually rather than in groups. Their diet consists mainly of other insects, but they also consume nectar and honeydew. 

Bull ants are highly territorial and will fiercely defend their nests. The nests are typically found underground and can be extensive, with numerous chambers and tunnels. 

Despite their fearsome reputation, bull ants play a crucial role in their ecosystem, helping to control pest populations and pollinate plants.


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