Nocturnal Bull Ants Use Polarised Moonlight for Navigation

Context: Scientists have discovered that two nocturnal bull ant species, Myrmecia pyriformis and Myrmecia midas, navigate at night using polarised moonlight.

What is Polarised Light?

• Light from the sun and moon normally spreads out in all directions. This is called unpolarised light.
• When this light passes through the Earth’s atmosphere, it scatters and becomes polarised.
• Polarised light means the light waves are organised in a specific direction, creating a pattern in the sky. This pattern is called E-vector pattern.
• Some animals, like ants, can see this pattern and use it like a built-in compass to navigate.

Why is Polarised Light Important for Nocturnal Insects?

• Many insects, like ants and bees, use the moon’s position to move around at night.
• However, the moon isn’t always visible—it changes shape (waxing and waning), gets covered by clouds, or is blocked by trees.
• Polarised moonlight, even though it is much dimmer than sunlight, still creates a pattern in the sky.
• Some insects can detect and follow this pattern, helping them find their way even on dark nights.

How Do Bull Ants Use Polarised Moonlight to Navigate?

• The ant species Myrmecia pyriformis and Myrmecia midas were known to use polarised sunlight to navigate during the day.
• But scientists didn’t know how they found their way at night after sunlight disappeared.
• They noticed that:
  • Midas ants returned home late at night.
  • pyriformis ants were more active on full-moon nights.

New Discovery

• Scientists found that these ants can see and follow polarised moonlight, just like they use polarised sunlight.
• Even when the moon is very dim (like during a crescent moon, when it’s 80% darker), the ants could still find their way.
• The pattern in moonlight’s polarisation acts like a hidden map, guiding the ants home.

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