As twilight settles over Sydney, Australia, a remarkable nocturnal ritual unfolds among the bull ants of the species Myrmecia midas. Emerging from their nests as the sun dips below the horizon, these industrious insects venture into the trees with purpose. Their mission: to hunt other insects, gather tree sap, and collect resources, all before returning to the safety of their nests before dawn breaks.
What sets these bull ants apart from many other ant species is their unconventional navigation method. While most ants rely on chemical trails left by their fellow workers to find their way back home, bull ants of the Myrmecia midas species forge their own individual paths. This solitary approach to navigation has long intrigued scientists, posing the question: How do these ants manage to navigate in the dark, without the aid of scent trails?
“It’s always kind of been this mystery,” remarks Cody Freas, a neuroethologist at Macquarie University in Australia.
Recent research has provided a groundbreaking answer to this puzzle: Bull ants utilize the moon’s polarized light as a nocturnal compass. Unlike humans, whose eyes perceive only certain wavelengths of light from the sun and stars, the uppermost part of bull ants’ eyes can detect patterns in the sky created by polarized light. This ability allows them to navigate even when celestial bodies are obscured by clouds or during periods of low moonlight.
In a study led by Freas and published in the journal eLife, researchers manipulated the polarized light pattern above the ants using a filter. By observing the ants as they returned to their nests in the wild, the scientists demonstrated that the insects were actively following this polarized light signal. This real-time adjustment in navigation suggests that bull ants rely on immediate sensory input rather than a static memory of their surroundings.
“The filter basically changes the entire sky above them,” explains Freas, emphasizing the direct impact of polarized light manipulation on the ants’ behavior.
Remarkably, the study revealed that bull ants can navigate by polarized moonlight even during a crescent moon, when the light signal is significantly weaker compared to a full moon. A full moon itself provides light that is one million times weaker than direct sunlight, yet this faint polarized signal serves as a reliable guide for the ants on their journey back home.
While dung beetles are known for using polarized light from the moon and stars to roll their dung balls in a straight line—a behavior termed celestial navigation—this is the first documented instance of an animal using polarized moonlight to navigate directly toward a fixed location, namely the bull ants’ nest.
As scientists continue to unravel the mysteries of animal navigation, the discovery underscores the remarkable adaptations and sensory capabilities of bull ants. It also highlights how different species harness unique environmental cues to thrive in their ecosystems.
Indeed, while the use of polarized light by bull ants for nocturnal navigation has long been suspected, this study provides conclusive evidence of its role. It opens new avenues for understanding how insects perceive and interact with their environment, shedding light on the complex strategies employed by animals to navigate their world, even under the cover of darkness.
