The Hoothi are a sapient fungoid species which feeds on decaying matter and are capable of assimilating and controlling dead bodies. Their ships are spherically-shaped organic dirigibles filled with noxious gas and which usually travel in hyperspace.
The Hoothi are composed of masses of individual white filaments which can move by themselves or hold together, forming a unified mind. They typically infect and kill sapient species to feed on their dead bodies and use them as hosts; but they can also infect a host passively for many years, broadcasting information from the host's senses into the Hoothi hive mind, or taking over and controlling the host's actions. They also absorb and assimilate the memories of those they consume (similar to the Wirrn, Blood Beasts or the Alzabo).
The Hoothi are extremely resistant to physical damage, including projectile weapons and fire. It is notoriously hard to kill them, as their regenerative abilities come from a cellular structure similar to the symbiotic nuclei of the Time Lords which allow them to regenerate.
Some billions of years ago the Hoothi were the masters of a powerful empire, harvesting sapient species as hosts on several planets. Their origins were unknown, but they were known as the master strategists of the galaxy and were involved in a war against the Time Lords.
- The New Doctor Who Adventures - Love and War by Paul Cornell (1992)