Mystery insect

a kind of butterfly? It sat still this morning at this spot but it had two red heads, on on each end. So it were two of this kind, having fun. By the time I came back with my camera, the fun was over, just one sat there resting ....
I discovered them while picking blackberries early in the morning. A grey but warm day is good for all the harvesting activities, that are starting right now. We have big amounts of red plums on the tree. Can anybody recommend a good recipe to preserve them?

Thank you very much for your wonderful comments, stars and hearts on my last picture. It warmed my heart!