The study was conducted to approximate the composition of house fly maggots and earthworms from different substrates as well as to evaluate their suitability as protein sources in the Nile tilapia (Oreochromis niloticus) diets. Chicken manure, cattle manure and fermented maize were used as substrates for production household fly maggots (HFM), while chicken, cattle and rabbit manures were used as substrates for production of earthworm meal (EWM). HFMs and EWMs with the highest protein content were used to formulate practical isonitrogenous diets (30% crude protein) containing graded levels of HFM and EWM meals (25%, 30%, 35% and 40%). The diets were fed to juveniles with an average weight of 2.6g in a growth trial that lasted for eight weeks. There were significant (p<0.05) differences in the crude protein contents between the HFMs as well as EWMs raised on three culturing media. Chicken manure produced HFM with significantly high protein content, while cow manure did the same for EWM. Growth and feed utilization was significantly higher in fish fed diets HFM35 and EWM35. The same diets were more cost effective to produce a unit of fish. Therefore, it is recommended to include either HFM or EWM meals at 35% in practical diets containing 5% fishmeal and cotton seedcake or any similar plant protein.