Context:
- Scientists found out that two types of night-active bull ants, Myrmecia pyriformis and Myrmecia midas, use polarised moonlight to find their way in the dark.
- This discovery is rare, with the Dung beetle being the only other animal known to do the same.
Polarised Moonlight Navigation in Bull Ants
- Ants relied on polarised moonlight for navigation under full, waxing, and waning moon phases.
- 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.
- When released midway, ants retain their sense of distance to the nest.
- Similarities with Solar Navigation: Strong similarities between solar and moonlight navigation suggest many insects use both light sources for orientation.
Role of Polarised Light in Navigation
- Both the sun and the moon emit unpolarised light.
- As light travels through Earth’s atmosphere, it gets scattered by air particles, becoming polarised.
- This polarisation pattern provides a natural compass for animals.
Significance of the Discovery
- Many nocturnal animals, like ants and bees, use the moon’s position for navigation, but the moon’s visibility can be inconsistent due to waxing and waning cycles, cloud cover, or tree canopies.
- Few animals use dimmer polarised moonlight for navigation, unlike the widely-used sunlight.
- Even under a crescent moon with 80% less intense moonlight, these ants can navigate using polarised moonlight.
- The discovery highlights the importance of polarised moonlight in navigation for certain nocturnal animals.
About Polarised Light
- Normal (Unpolarised) Light:
- Light waves vibrate in multiple directions.
- Polarised Light:
- Light passes through the atmosphere or reflects off surfaces like water or glass.
- Waves align in a single direction.
- Sunlight vs. Moonlight Polarisation:
- Sunlight:
- Strongly polarised as it scatters in the sky.
- Reliable navigation tool for many insects.
- Moonlight:
- Much dimmer and less polarised.
- Carries a consistent pattern detectable by certain nocturnal animals.
- Sunlight:
- Moonlight Polarisation:
- When moonlight enters Earth’s atmosphere, it is scattered by air molecules and dust particles, causing polarisation.
- 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:
| Type | Activity Period | Examples | Key Features |
| Diurnal | Active during the day | Humans, Butterflies, Eagles | Rely on daylight for vision and activity |
| Nocturnal | Active during the night | Owls, Bats, Leopards | Enhanced night vision or echolocation |
| Crepuscular | Active at dawn and dusk | Deer, Fireflies, Rabbits | Avoids predators, utilizes dim light |
| Cathemeral | Active at varying times | Lions, Bears, Lemurs | Flexible activity depending on conditions |
Source: The Hindu
Previous Year Question
Consider the following fauna:
1. Lion-tailed Macaque
2. Malabar Civet
3. Sambar Deer
How many of the above are generally nocturnal or most active after sunset?
[UPSC Civil Services Exam – 2023 Prelims]
(a) Only one
(b) Only two
(c) All three
(d) None
Answer: (a)
Explanation:
The Lion-tailed Macaque is a diurnal species, meaning it is active during the day.
Sambar Deer are primarily crepuscular, being most active during dawn and dusk.