I have seen boxes of Cordyceps in the "Expensive Chinese Medicines Boxed as Gifts" section of the supermarkets here (that is, a tiny amount of Chinese medicine in a huge, otherwise empty, box - it's not the value of a gift that counts here, size is important) but I'd never really paid much attention.
One of my colleagues recently received (and hastily returned) a box of Corsyceps Sinensis. I've been intrigued as to what they are exactly as they look a lot like a dried caterpillar with a stick up its arse. I don't know why I was surprised to find out that that's pretty much what it is, only even more sinister.
The Chinese name on the box was 冬虫夏草, that is Winter Insect Summer Grass. Doesn't sound too bad does it.
Wikipedia puts it like this: ... the fungus infects the caterpillar... Once inside the fungus mycelium ramifies through the host tissue, eventually completely consuming it and replacing the caterpillar body with fungal tissue. At this stage, the fungus grows a usually columnar fruiting body that reaches the surface and releases spores.
So, the medicine is actually the shell of a caterpillar that has been consumed by a flesh eating fungus. Sounds tasty. If you're contemplating eating some, perhaps you might like to watch this video about Cordyceps first. Yum.