Here are four more shots, done to document the phenomenon rather than for critique (although critique is always welcome of course)
The first shows the scribble under new bark. The beetle may have been at work under there at the time.
The second and third show the scribble on a trunk from which a layer of bark has peeled off and fallen.
The fourth shows the traces of a much larger insect, some kind of grub I suspect.
I think the lines are beautiful and that any quality in photographs of them is largely due to the work of the original artists (the insects)
I also think one of the pleasures of photography is that it encourages a close engagement with the natural world.