Half plant, half animal, Cordyceps is a wonder of nature. The Chinese name for Cordyceps Sinensis, dong chong xia cao, means winter worm, summer grass. The spores of the Cordyceps fungus infect and grow in the body of a caterpillar, inspiring it toward strange behaviors. Eventually, the caterpillar dies and out of its head sprouts the head and stem of the Cordyceps. Such a dramatization of the transformation and continuity of life must have inspired man to investigate its medicinal properties. Cordyceps tonifies both the yin and the yang. It is an important herb for chronic pulmonary problems such as bronchitis. Like ginseng, it is used as an anti-aging herb because it can boost immunity to promote health under stress.
There are thousands of varieties of Cordyceps. Their parasitic life process is similar but their hosts are unique. Here is some footage showing one that takes over the bodies of jungle ants. Fascinating but maybe not for the squeamish:
http://www.youtube.com/watch?v=XuKjBIBBAL8&NR=1&feature=fvwp