Birch fungus is a general term for a type of bracket fungus that grows on birch trees, willow and red willow (alder) shrubs. As medicine. Birch fungus was cut up, boiled and used for stomach ailments. Ashes were rubbed gently on skin sores and pimples.  As tobacco. The fungus was also cut up and crushed into small pieces, and then mixed with cigarettes or chewing tobacco to make it last longer.  As insect repellent. Pieces of birch or willow fungus were burned on a plate to repel mosquitoes.  As moth ball. A small piece of willow fungus can be used as a moth ball in a closet or drawer.  As fire starter. Once dried and pounded, birch fungus makes a good fire starter that can be ignited with a flint and steel.