Its spores germinate in the autumn and spread through the caterpillars 'bodies, finally causing them to die and go stiff. The hyphae form sclerotia (compact masses of mycelium) inside the caterpillars' bodies, and in this form the fungus remains dormant through the winter. The following summer, thin, erect fruiting bodies grow out of the caterpillars, creating the part of the fungus generally referred to as "grass."
蟲草菌的子囊孢子在秋季發芽，穿入幼蟲體內增生蔓延，終使幼蟲僵死，菌絲體在蟲體內形成菌核過冬，次年夏季再從蟲體內伸出子實體，也就是一般稱為「草」的部分。