In the life cycle of the silk moth, the larval stage lasts for how many days?

The egg is the first stage of the silkworm's life cycle. The egg is laid by the female moth. At one time, a female moth lays up to 350 eggs. The eggs hatch due to the warm air in the spring releasing a hairy silkworm. This is the second stage also known as the larval stage. At this stage, the silkworms grow enormously feeding on mulberry leaves for roughly 25-30 days before moving on to the next stage. 

After 25-30 days the larvae form a protective covering around themselves called the cocoon which is the next stage.