Mosaikum links to the Deutsches Forschungszentrum für Schmetterlingswanderungen, where you can record sightings of moths and butterflies and they are marked on a map of Germany (in German).
I mention this because my second-most-popular entry of all time is the recording of a sighting of a humming-bird hawk moth, Macroglossum stellatarum. I eventually closed the comments (or thought I had), because I was getting sightings of (to me) less tasteful objects cropping up there.
I wasn’t even really aware of migrating moths, although I’d often read about monarchs in North America. About the humming-bird hawk moth, the RSPB says ‘keep your eyes peeling for these amazing visitors’. The German site classes it under ‘Spinner und Schwärmer’ (other classes are Tagfalter, Eulenfalter and Spanner) – it all goes to show words can have more than one meaning.
In case you’re wondering, my most popular entry is the one on how Ikea chooses the names for its furniture.