Emperor Moth Caterpillar Saturnia pavonia
When fully grown, the Emperor moth caterpillar is as long and nearly as wide as a human finger. It has black hoops when younger but loses these when fully grown.
It has orange/yellow/pink protruding spots with black spines on its green body.
The caterpillar spins a silk web enclosing itself in a sheltered place in heather or bramble to begin its 7-8 month pupation.
The caterpillar develops the web into a strong cocoon round itself to keep it safe from predators while it turns into a pupa.
Link to Emperor moth