A timekeeper for siesta

Circadian clocks must be flexible and they must be able to adapt to varying environmental conditions. Otherwise, it would be impossible for living beings to change their patterns of activity when the days get shorter again as is happening now. After all, Drosophila, also known as the common fruit fly, no longer needs a long siesta in autumn to protect itself from excessive heat and predators as in the middle of summer. At the same time, the fly must shift its evening activity peak a few hours forward if it doesn't want to end up buzzing around in the dark.