Sun Compass on Demand

A tethered flying monarch butterfly orients in the flight simulator with respect to a green light spot. While flying, microelectrodes record the butterflies' brain activity. (Image: Jerome Beetz / Universität Würzburg) 11/24/2021 - Monarch butterflies employ a sun compass on their long-distance migration. Surprisingly, a new study shows that the compass is only established during flight. Monarch butterflies are famous for their annual long-distance migration, which takes them over several thousand kilometres from the north of the USA to their overwintering habitat in central Mexico. On their migration, the conspicuously orange-black-white colored butterflies use sun information as main orientation reference. But how is sun information processed in the butterfly's brain? Previous studies have already described cells that process the solar azimuth. "However, we didn't know these cells encode the sun during flight," says Jerome Beetz from the Biocentre at Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany. Until now, it was assumed that the sun compass always works - irrespective of whether the insects sit, walk or fly. A team led by JMU researchers Jerome Beetz and Basil el Jundi shows in the scientific journal Current Biology that this is not the case and that the compass is established at the onset of flight: "Surprisingly, the nerve cells change their coding strategy during flight, so that the neural network represents the heading direction of the butterflies relative to the sun in a similar way to a compass. This only happens when the animals can control their own direction of flight." - Butterflies in a flight simulator . How was this gap in knowledge closed?