Dysstroma citrata
Dark Marbled Carpet 
The caterpillar illustrated was found on the 
  underside of a leaf of the Himalayan Bramble Rubus discolor, where it 
  spent most of its time, rarely venturing to the upper side. Indeed, the caterpillar 
  appeared to be rather bashful, and often rested in the "bashful" mode 
  evident in one of the photographs. Although this habit is not quite unique to 
  the genus, it can be used as a first guess for identification. I have also found 
  the caterpillar on the underside of the leaves of Stinging Nettle. Caterpillars 
  found in early April have metamorphosed to moths by late May. The moth occurs 
  in Europe as well as in North America.