I have a small freshwater aquarium at home with only some aquatic plants at the moment. In the summer, I put some mud and sand from a local pond into the tank. At some point, I noticed a strange moving "segment" of plant:
Here is a video of it moving right under the surface of the water:
If you look closely, you can see that the "segment" is actually made from several smaller segments of a stem of an aquatic plant. In other words, this little creature chopped up the plant, then assembled this little "tube" for itself to hide.
Few weeks later, it apparently disassembled the little house and created a larger one from leaves:
Here is a video of it:
It basically this little leafy house everywhere and can move up and down the water column. I think it feeds on different plants because I can see some visible damage in the tank.
Can you identify this creature? The location is northern Europe.