In both T. angusti-collis and T. nevadensis only the soldier caste is developed during the first 3 or 4 years, or until the population totals approximately 450 individuals. Hence, in colonies comprising from 50 to 75 members, it is certain that none of the population belongs to the reproductive caste. A careful examination of several communities of this type proves that the young of each species are all alike at the time of hatching, that they undergo 4 molts, and hence the adult soldier is in the 6th instar. The main features of each instar are described in detail.