CBSE Class 7 Answered

All insects go through a series of changes as they mature. This process is called metamorphosis. The first stage is the ovum or egg, second stage is the larva or caterpillar, third stage is the pupa and final stage is the imago or adult. Before entering the pupal stage, a silkworm weaves a net to hold itself. The movements of the head of the silkworm secrete a fibre made of protein which hardens on exposure to air and becomes silk fibre. Soon, the caterpillar spins a covering called cocoon from silk fibres which protects the pupa. The further development of pupa into moth continues inside the cocoon. An adult silk moth emerges from the cocoon.