The dark head and ventral plates are diagnostic features of E. atricollis larvae, the ventral plates being far more obvious in the early/intermediate instars. The image illustrates the same larva and mine photographed a week apart, the image from 23rd Sept. showing the fully mature larva exiting the mine.
On Salix fragilis, Halesowen, VC37. September 10th 2019.
Although this mine began in a leaf it then travelled 20cm up the stem before moving to a second leaf and pupating two thirds the way along the leaf edge.