sorry three responses haha... didn't see the bottom two pictures. Apparently the scroll feature is not over-rated. Thanks for posting this, I am not 100% confident on what the predator is and wish I had the opportunity to see it in person. My best guess is a weasel... I don't know where you are from but I'm assuming least weasel to be able to fit into the vole's burrow. Weasels have an innate instinct to kill as much prey as possible if the opportunity arises. The reason they do this is because they have a high metabolism and take the protein as they can. If they have excess food they will sometimes only eat the brains or in most cases they will store the food for a later time. Fishers also make food caches and a few others in the weasel family. I believe this picture shows a weasel's "cache." I don't think the weasel will come back and finish off the vole family because i'm sure some bird or insect will get at them first (especially because it seems like you live in a pretty warm area). Still... it may... Pretty awesome find and it seems like you found a natural pest control! no more trapping!

It's a Sea Cucumber, an invertebrate that feeds on decaying organic matter. There are many different species. https://en.wikipedia.org/wiki/Sea_cucumber

I think the magic scientists who make the physiologies match could deal with the strings. As it is, most guitar strings are synthetic and/or metal. Harp strings are also made of nylon and/or metal. Piano strings are metal. Violin strings are also mostly synthetic and/or metal, though sheep's gut is still used sometimes for authentic historical sounds. The sticking point is the bow. Current synthetic bow filaments are too smooth and not as well liked as real horsehair, but that doesn't mean that they couldn't be made better. It's just not worthwhile to develop specially to imitate horsehair while horses are still being slaughtered in sufficient quantity to provide the real thing.

Picture?