The vast forests of Lepiota and their gigantic Fungi were known since ancient time as the primary blooming ground of Mushei.
As such it is not a surprise that a lot of Mushei decided to live in the forest they bloomed. But as they were not the only inhabitants of this forest, dangers lurked.
The security in numbers made the Mushei band together and form communities. They weren't anything concrete yet, just friends and families choosing to stay close.
They chose to live high in the gigantic mushrooms and underneath the surface creating a tunnel system to travel through the forest safely.