Polarised Moonlight for Navigation

Scientists at Macquarie University, Sydney, discovered that two nocturnal bull ant species, Myrmecia pyriformis and Myrmecia midas, navigate at night using polarised moonlight.

• This is only the second known instance of an animal using polarised moonlight instead of sunlight for orientation after the Dung beetle.

Results and Findings 

• Navigation Using Polarised Moonlight: Ants relied on polarised moonlight for navigation under full, waxing, and waning moon phases. Their accuracy varied with the moon’s phase and was ineffective when the moon was absent.
• Internal Distance Tracking:  Ants continuously update their distance vector while traveling. Even when released midway, they retain their sense of distance to the nest.
• Similarities with Solar Navigation: Scientists found strong similarities between solar and moonlight navigation in ants. This suggests that many insects use both light sources for orientation.

Role of Polarised Light  in Navigation

• Formation of Polarised Light: Both the sun and the moon emit unpolarised light. As light travels through the Earth’s atmosphere, it gets scattered by air particles, becoming polarised.
  • This polarisation pattern provides a natural compass for animals.
• Differences Between Sunlight and Moonlight
  • Sunlight is strongly polarised and widely used by insects for navigation.
  • Moonlight is much dimmer but still carries a consistent polarisation pattern that certain nocturnal animals can detect.

Significance of the Discovery: 

• Importance for Nocturnal Animals: Many nocturnal animals, such as ants and bees, rely on the moon’s position to find their way.
  • However, the moon’s visibility is inconsistent due to waxing and waning cycles, cloud cover, or tree canopies.

• Unique Use of Polarised Moonlight: Unlike sunlight, which many animals use for navigation, few animals use the much dimmer polarised moonlight.
• Even under a crescent moon, when moonlight is 80% less intense, these ants could still navigate using polarised moonlight.

Moonlight Polarisation

• When moonlight enters Earth’s atmosphere, it is scattered by air molecules and dust particles, causing polarisation.
• The degree of polarisation varies based on the moon’s phase:
  • Full moon: Low polarisation due to stronger light intensity.
  • Crescent moon: Higher polarisation since the light is dimmer and scatters more efficiently.

Types of Species Based on Time of Activity