A small, smooth, undistinguished green caterpillar feeding on stinging
nettle - not a chance of identifying it. Could be any one of hundreds of species.
But count the mid-abdominal prolegs! Only three pairs instead of the usual four!
It is one of the snout moths of the genus Hypena. The picture of the
adult moth showing the conspicuous elongated palps shows why these moths are
called "snouts". The caterpillars are easy to rear (as long as you
don't mind a few nettle stings), and they produce moths within a few weeks of
finding the caterpillar.