What is this insect (Germany)?
It's hard to tell from your photo, but you should check whether Macroglossum stellatarum (German: Taubenschwänzchen/ English: hummingbird hawk-moth) looks similar to what you've seen. 

This moth is living in Germany (and other regions) and due to it's way of flying (hovering and audible humming) it's sometimes confused with a hummingbird.