Cocoon
When the caterpillar is fully mature it spins a dark brown silken cocoon on a branch which usually has a leaf to protect it with. When spinning is complete, the caterpillar sheds its final skin and takes the form of its pupal life stage. Within a day of spinning completion, the cocoon sets to a hard waterproof shell with a rough exterior and a smooth interior wall. Air holes can be seen along the side of the cocoon indicating that the cocoon is probably otherwise airtight. The moth usually emerges from the cocoon the following year (in Spring or early Summer) but depending on weather conditions can stay in the cocoon from anywhere between two and five years. One case has even been recorded of a moth emerging out of the cocoon after 10 years.
When the metamorphosis is complete, the adult moth regurgitates a fluid to soften the tough cocoon and then cuts a hole using sharp hooks on the base of each forewing. The effort to release itself from the cocoon is vital for its wings to expand and dry after emerging. Pupae cut from the cocoon will hatch, but the moths' wings will never expand.
Read more about this topic: Opodiphthera Eucalypti