My system is suffering this summer and one of the symptoms is infestations of bugs on my veggies. I have an abundance of Harlequin Bugs which are fairly easy to identify, but I also have a lot of these worms that are eating both chard and kale. Yes, the picture does show some webbing and when picking these by hand I have occasionally seen one trying to escape by spinning a thread to lower itself down.
Thanks, I had looked at pictures of cabbage worms but these looked different. But of course there are many variations within a specie. Unfortunately they don't seem to be affected by BT.