They look like they would be custom-made storage shells for beetle's wings!  Perhaps when the beetles fly from Denmark to America (on an airplane) they pack extra wings in these little suitcases.  Just in case the first pair gets wet when they go to the beach ... you know, how you do!  :)

Oh Helle ... I am at a loss!  I think perhaps these exist only in your country. 

Okay, here is my next question.  You can ignore everything else, I'm just thinking out loud:

Do they have anything to do with insects?  They look quite small.

"If your pictures aren't good enough, you're not close enough."  ...  Robert Capa