Australia’s Bogong moth uses a stellar compass with help from Earth’s geomagnetic field to stay on course across about 620 miles to cool alpine caves, according to a new study.
The work shows that the moths can distinguish specific geographic directions at night using the starry sky alone.
Billions of bogong moths head for high country each spring, then reverse the journey in autumn after months of aestivation in cave walls. The feat is precise, seasonal, and inherited rather than learned.
Professor Eric Warrant of Lund University led the research with collaborators across Europe and Australia.
Moths navigate by stars
The team ran night flights in a rural, non-magnetic laboratory using a custom flight simulator that projected a natural star field above tethered moths, while removing magnetic cues so only the sky pattern could guide flight. They also ran outdoor tests under real skies to confirm the behavior in the field.
“When the starry sky was rotated 180 degrees, the moths also changed direction 180 degrees, but when the stars were distorted, their orientation disappeared. It was a real eureka moment to experience this in the experiments,” said David Dreyer, a researcher at Lund.
“Navigating by the stars is a capacity that only humans, often with the help of a sextant, and certain birds that migrate at night possess. Now we can establish that the Bogong moth is the first invertebrate so far known to master this feat,” said Warrant.
Why moths rely on stars for journeys
The night sky shifts across hours, yet the moths held their inherited course when the stars moved across the dome. That suggests they are extracting a stable cue from changing patterns.
Birds have long been shown to use star patterns, a result established in classic planetarium experiments with indigo buntings.
Moths now join the list of celestial navigators, but with a key twist, because they use the stars to aim for a specific geographic bearing, not just to keep a straight line.
Short range sky use is not unprecedented in insects. Dung beetles orient using the Milky Way to roll in a straight line away from competitors at the dung heap, which is a different task from long distance navigation to a fixed destination.
Moths switch to magnetic cues
On overcast nights, the moths still maintained their seasonally correct heading in field tests, a pattern consistent with a magnetic compass that steps in when the sky is hidden. That redundancy makes sense for nocturnal travel that can span many nights.
Earlier work in 2018 had already shown Bogong moths sense and use Earth’s magnetic field to steer, aligning magnetic and visual cues when they agree and losing orientation when the cues conflict.
The new results show that either cue alone can be sufficient, with stars taking the lead under clear skies.
How moths decode sky patterns
The study did not stop at behavior. The team recorded activity from visual neurons that responded when the projected star sky rotated, and those responses vanished when the stars were randomized, indicating tuning to natural celestial structure rather than generic motion.
Some cells peaked when the moth was oriented toward a common sky direction, which hints at how the brain encodes a stable heading from complex light patterns. The responses appeared in regions that interconnect sensory input with motor steering.
One navigation hub, the central complex, is known across insects as a circuit that computes heading and desired direction, and the new data are consistent with that role.
The pattern suggests a compact neural solution for fusing sky and magnetic information into a single steering command.
A plausible magnetic sensor
How an insect detects a weak magnetic field is still an open question. A leading hypothesis proposes a light dependent chemical reaction in cryptochrome proteins that forms magnetically sensitive radical pairs, which can change reaction yields depending on field orientation.
There is direct experimental support for cryptochrome-based magnetic sensing in another migratory insect, the monarch butterfly.
In this species, CRY1 mediates light-dependent inclination responses under Earth-strength fields and relies on both the antennae and the eyes as magnetosensory organs. Bogong moths may use a related mechanism, although that remains to be nailed down.
Future research directions
The findings raise the bar for what a small nervous system can do. A moth brain smaller than a grain of rice can extract compass information from dim, complex star fields and keep it calibrated with a magnetic fallback.
The approach is robust, portable, and cheap in energy. It also highlights why dark, clear skies still matter for nocturnal migrants that rely on faint celestial structure.
Two puzzles stand out. How do these moths decide they have reached the right mountain caves, and which local cues trigger the stop after the long haul?
There is also the question of calibration. The system likely needs a way to keep sky and magnetic compasses aligned over time, and to decide which to trust when the cues disagree.
The study is published in the journal Nature.
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