The Castor plant (Ricinus communis) is an important oilseed crop, is highly vulnerable to Spilosoma obliqua (Walker), a lepidopteran insect pest also known as Bihar hairy caterpillar or Jute hairy caterpillar. It is a polyphagous pest infecting a wide range of as many as 126 species belonging to 24 plant families that are economically important including pulses, oilseeds, cereals, and gram. The Spilosoma obliqua caterpillar feeds gregariously on Castor leaves and causes significant loss to the crops. In this study, the life cycle of Spilosoma obliqua was observed in laboratory conditions by feeding fresh Castor leaves. The study reveals that the entire lifespan of Spilosoma obliqua ranged between 39 and 46 days. The eggs laid were slightly greenish, and the number of eggs per batch was 130 to 250. The period of egg incubation ranged from 6 to 8 days. The larval development had 6 instars before pupation. The duration of the pupal stage ranged from 8 to 12 days. Adult moth appeared slight light brown with many black spots on wings and red abdomen. The longevity of adult male moths and female moths was 3-5 days and 5-8 days respectively. Male and female moth could be identified by tapered and blunt abdomen respectively. During life cycle observation on Castor leaves, Spilosoma obliqua was parasitized by Propanteles oblique (Hymenoptera: Braconidae).