Muga silk is known as the 'golden thread.' Here's why a sari made with this silk can cost $6,500.

Unlike any other fabric, muga silk has a naturally lustrous gold sheen. It comes from the cocoons of muga moths that feed on som trees. A saree made with muga silk can cost $6,500, thousands more than other saris. But the caterpillars needed to make it are in danger. So what's happening to the muga silkworm? And why is this silk so expensive?