However, there is another striking thing about these words.
English : Butterfly
Swedish : Fjäril
Danish : Sommerfugl
German : Schmetterling
French : Papillon
Italian : Farfalla
Spanish : Mariposa
Portuguese : Borboleta
They are all totally different! Even in closely related Western European languages, where otherwise most terms tend to derive from a common Romanic or Germanic root.
I have no idea why this is, and don't know any other examples like this.
Apparently, the Dutch word is "vlinder", which once again is completely unrelated to the rest, but this is the only one I had to look up in a dictionary so I cannot really vouch for it. I guess I don't listen to a lot of Dutch popular music.