What are haustoria?
Hustoria is the appendage or portion of a parasitic fungus or of the root of a parasitic plant that penetrates the host's tissue and draws nutrients from it. Haustoria do not penetrate the host's cell membranes.
Fungi in all major divisions form haustoria. Haustoria take several forms.
On penetration, the fungus increases the surface area in contact with host plasma membrane releasing enzymes that break down the cell wall, enabling greater potential movement of organic carbon from host to fungus. An insect hosting a parasitic fungus such as Cordyceps may look as though it is being "eaten from the inside out" as the haustoria expand inside of it.