The immature stages of Bittacus planus Cheng, 1949, including egg, four larval instars, and pupa, are described and illustrated for the first time. The egg is spherical, with two types of micropyles. The larva is eruciform and peripneustic, bearing eight pairs of prolegs on the abdomen. A pair of compound eyes and a median ocellus are present on the head. Each segment of the abdomen has rows of protuberances bearing setiferous clavate setae. The pupa is exarate and decticous. The species is univoltine, overwintering as diapausing eggs on the ground. Larval duration, including a prepupa of 10 days, lasts about 30 days. Pupation occurs in a soil cell, ranging from 10 to 15 days. The roles of larval compound eyes and the ocellus in the phylogeny of Holometabola are briefly discussed.