Nine larval instars of Simulium ociveps Edwards are discriminated using morphological and biometrical characters. The labral morphology of 1st and 9th instars is given in detail. Simulium tahitiense Edwards probably also has 9 larval instars, but only the first 5 and last instars could be discriminated by morphological characters. The identification of remaining instars is based on peaks in the frequency distribution of larval head widths. Some larvae taken in this study were tentatively assigned to Simulium cheesmanae Edwards, a species previously unknown in the larval stage. The relationships and biology the Tahitian simuliids are briefly discussed. It is suggested that the larval head of S. oviceps is apomorphic in relation to the larval heads of the other Tahitian simuliids.