A timekeeper for siesta

External stimuli can rearrange the hierarchy of neuronal networks and influence behaviour. This was demonstrated by scientists from the universities of Würzburg and Brandeis using the circadian clock of the fruit fly as an example. 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 least in our latitudes. 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. For the fruit fly to adapt to changing day-and-night rhythms, its circadian clock must be able to process external cues, so-called zeitgebers, which are used to synchronise the molecular and physiological properties of the organism.