Caterpillar fungus is a hybrid of a fungus that kills and lives in caterpillars. It has been used in traditional herbal medicine for many centuries but has gained popularity in recent decades. It can sell for up to 3 times its weight in gold. The high demand has driven up the price, which can be as much as about $63,000 per pound. Some towns in the Himalayas rely on collecting and selling this fungus for a living.