Hypena californica

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.