Synthetic laboratory strains of two species of flour beetles, Tribolium castaneum and T. confusum, were compared in terms of the voracity of larvae for eggs. Significant differences were observed between the species. Tribolium castaneum was much more cannibalistic with the greatest difference observed in 4— to 14—days—old larvae. Older active larvae of both species ate more eggs than did younger larvae. No significant differences were observed in the choice of eggs of both species when they were offered at the same time, but slightly more T. castaneum eggs were consumed than T. confusum eggs when larvae were supplied eggs of a single species. In one experiment a control series was maintained in the same manner as the experimental series, except that the larvae were not given eggs. Fecundity of adult T. castaneum emerging from these larvae was lower than in adults from the experimental series which had fed on eggs during the larval stage. No such difference was observed between experimental and control groups in T. confusum. It is suggested that differences in egg cannibalism by larvae of the two species of flour beetles may account in part for the superiority of T. castaneum in competition with T. confusum under the given conditions (29°C, to to 70% R. H.).