Study
Antennal Circadian Clocks Coordinate Sun Compass Orientation in Migratory Monarch Butterflies
Merlin, Christine; Gegear, Robert J.; Reppert, Steven M.
Science, 2009
Migrating monarchs were flown tethered in a flight simulator that records heading. Antennae were removed, or painted with black or clear enamel, and the butterflies were tested after clock-shifting.
- Studied in
- Danaus plexippus
- Sample size
- tethered monarchs in a flight simulator
Removing the antennae abolished time-compensated orientation while leaving flight intact; painting them black — blocking light to them but leaving them attached — did the same, and clear paint did not.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The circadian clock that time-compensates the monarch sun compass sits in the antennae rather than in the brain, and it is entrained by light reaching the antennae.
How NatureHQ reads it
A result that is strange enough to be worth the page on its own: the clock a monarch steers by is in its antennae, and the black-versus-clear paint control is what turns an amputation result into a demonstration about light. Cited for the mechanism of the clock, not for the route the butterflies take.
- Tethered flight in a simulator, which measures intended heading rather than a journey.
- Shows where the clock is, not how the compass output is used over thousands of kilometres.
Painting a butterfly’s antennae black
Where is the clock that lets a monarch correct for the moving sun?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Animal navigation
The sun moves, so using it as a compass means knowing the time. Shift an animal’s internal clock by six hours and it sets off about ninety degrees wrong — confidently.
Monarch butterfly
The clock a monarch uses to correct for the moving sun is not in its brain. It is in its antennae, and painting them black stops the compass working.
Published by: American Association for the Advancement of SciencePublished in Science or Science Advances (AAAS).
doi.org/10.1126/science.1176221
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.