It looks like a thin leaf in this picture, but that’s the little villain in the center of this photo. And that dark stuff that is sprinkled throughout the webbing. Ten guesses what that is. And the dark patch just above the little worm? That’s the remains of its dinner (and lunch and breakfast).
The only good thing about these little critters is that they grow up and fly away. Until this spring I’ve only seen them on the white dawn climber in the front garden. I’ve pinched off all of the ones I’ve been able to reach and I suspect my careful pinching last spring reduced the number of larvae that I had to smoosh this year. I’ve only found a couple on the hansa roses. The larvae in the photo above was one of them.
Sawflies have saw-like ovipositors that allow them to saw into foliage so they can lay their eggs.