In hot weather, flies blow water bubbles so they cool via evaporation, before re-ingesting them. But on 7ºC days like today, it's to increase the concentration of their liquid food. Same process, different purpose.
I believe this is a species of tiger fly, Coenosia agromyzina.
#Heidelberg 🏰
#Photography 📷️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️️
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