Impact of crowding during the larval period was studied using a population of Philosamia ricini Hutt (Lepidoptera: Saturnidae), commonly known as Eri Silkworm. Eri silkworm is an economically important species, as its fiber is used in the textile industry and the pupae serve as a delicacy. This study showed that crowding affected the growth of larvae because as the densities increased the growth rate decreased and the duration of larval development was lengthened. The larval weight decreased and the size of the cocoons was also affected, showing a positive correlation with the other parameters. The emerged moths were smaller in the denser lot than in the less dense lots. The emergence of the moths was delayed in the denser regime. As the density increased the fecundity decreased. Fiber quality was studied by Instron Tensile Tester and it was found that the larvae reared in small numbers showed high tensile properties. This study suggests that during rearing of Eri, silkworm crowding should be avoided by providing an optimum condition as it affects the silkworm ecologically and economically.