Atmospheric plankton
Some species of spiders use them to travel.
They climb into a tall spot, release a long thread into the wind. and then just let go of their perch. Some have been collected in the stratosphere. That's how some species have been able to colonize tall mountain ranges, or oceanic islands.
It doesn't look like this one is in a wind, though. It looks like a still day and its rising straight upLike a skyhook.
Could you determine how high it went, or did it just go out of sight? And how were you able to photograph it? Is that the sun glinting off it?