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Nocturnal Bull Ants
Context:
Many nocturnal animals, including insects such as ants and bees, rely on the moon’s position to navigate while foraging.
Nocturnal Animals
These animals are active at nighttime and sleep during the day. They have adapted unique traits to survive in the dark, helping them avoid predators and find food. Examples of nocturnal animals include owls, bats, foxes, hedgehogs, and raccoons.
Adaptations of Nocturnal Animals:
- Vision: Nocturnal animals often have larger eyes and wider pupils to collect more light, improving their sight in the dark. Their eyes contain more rod cells than cone cells, enhancing their ability to see in low-light conditions. Some animals, like cats and foxes, possess a tapetum lucidum, a reflective layer behind the retina that reflects light and gives the rods a second chance to absorb it. This reflective layer causes their eyes to glow in the dark.
- Hearing: Many nocturnal animals have enhanced hearing to navigate in the dark. Some have cupped ears to capture more sound, while others, like owls, have asymmetrical hearing to pinpoint the exact location of sounds.
- Smell and Taste: Nocturnal animals often rely on their sense of smell or taste to locate prey. Raccoons have a great sense of smell, while snakes use taste to find their prey.
- Echolocation: Bats use echolocation to find prey by emitting sounds that bounce off objects. The intensity and pitch of the returning sound help them determine the size and distance of their prey.
- Bioluminescence: Some nocturnal creatures, like fireflies, produce their own light for communication, finding prey, and defense.
- Camouflage and Stealth: Nocturnal animals often have dark or patterned coloration to blend into the shadows, helping them move unseen. They may also exhibit slow and deliberate movements to avoid detection. Owls, for example, have special feather adaptations that allow them to fly almost silently, making them formidable hunters.
More on News
- However, since the moon follows a waxing and waning cycle and can be obscured by clouds or dense tree canopies, tracking its exact position is not always possible.
- Now, for the first time, scientists at Macquarie University, Sydney, have discovered that two species of nocturnal bull ants (Myrmecia pyriformis and Myrmecia midas) navigate at night using polarised moonlight.
- This type of light, though significantly dimmer than regular moonlight, contains distinct patterns that provide orientation cues.
Role of Polarised Moonlight
- Seen from the ground, both sunlight and moonlight exhibit characteristic polarisation patterns.
- These patterns, rather than the location of the light source alone, serve as a natural compass for certain animals.
- The study found that nocturnal bull ants detect and use polarised moonlight for navigation throughout the lunar cycle, even when the moon is only a crescent, with an 80% reduction in brightness.
- This is particularly significant because moonlight’s polarisation patterns are nearly a million times dimmer than those in sunlight.
- While many animals are known to use polarised sunlight for orientation, the only other known instance of an animal using polarised moonlight is the dung beetle.
Science Behind Polarisation
- Both the sun and the moon emit unpolarised light.
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- Light waves consist of electric and magnetic fields oscillating perpendicular to each other and to the wave’s direction of motion.
- When this light passes through the Earth’s atmosphere, it is scattered by air particles and becomes polarised, meaning the electric field oscillates in a fixed plane.
- The scattered light forms a unique pattern in the sky, known as the e-vector pattern.
- Researchers found that when the sun or moon is near the horizon, this pattern aligns approximately parallel to the north-south axis, creating a stable navigational cue for animals that can detect it.
Experimental Evidence
- To test the ants’ response to polarised moonlight, researchers projected linearly polarised light onto a population of nocturnal bull ants in their natural habitat.
- They then observed how the ants navigated between two nests located over 50 metres apart.
- During full, waxing, and waning moon phases, researchers rotated a polarisation filter clockwise by 45° and later counterclockwise by 45°.
- Each time, the ants adjusted their paths in response to the altered e-vector of the light.
- Once they exited the filtered light, they reoriented themselves according to the natural polarisation pattern in the sky.
- Paired statistical tests were used to analyse the shifts in navigation angles.
- The magnitude of the shifts was measured as the number of degrees the ants altered their heading when exposed to polarised light.
- Interestingly, while the ants consistently used polarised moonlight, their heading shift magnitudes were lower during the waning moon phases, a finding that surprised researchers.
- Foraging ants showed greater shifts during the waxing full moon and waxing quarter moon compared to waning phases.
Impact of the Lunar Cycle
- Under a new moon, when ambient polarised moonlight is absent, the ants’ paths did not significantly change when the filter was rotated, nor did they reorient their paths once they exited the filter.
- This suggests that without moonlight, the ants rely on alternative cues for navigation.
- Another statistical test was employed to compare differences in shift magnitudes when the filter was rotated in different directions across various lunar phases.
- During a full moon, when moonlight reaches 80% of its maximum intensity, the shift magnitudes ranged from 36.6º to 43º at one nest and 21.5º to 28.9º at the other.
- The difference was attributed to the varying distances the foragers traveled; ants from the first nest had a longer path (6 m) compared to those from the second (2.5 m).
- Researchers noted that at shorter distances, sky compass-based navigation becomes less reliable.
The study raised new questions about how these ants integrate lunar polarisation cues into their navigation. The researchers speculated that the ants might track the lunar compass using time-compensated calculations or by referencing other environmental cues, such as surrounding landmarks, similar to honeybees and desert ants.
