Dusk

The Galactic Scourge
First discovered on Gelidia, the Dusk are a race of sapient airborne mycelium that infects and controls other organic life. They fight for control of biomass within their sparse, stratified societies of Dusk Brains. Dusk Brains control clouds of Dusk and all the creatures that it has infected. They range in size from a human's chest to the largest living being in all of human history: The Dusk God.

Dusk are capable of interstellar travel and they spread from world to world after taking control of a planet's entire biosphere. Dusk are considered humanities greatest threat above all other aliens.

Biology
What can be called a single Dusk organism is made up of three distinct parts: The Cloud, The Brain, and The Servants.

The Cloud
The main body of a Dusk is its mycelium cloud. The cloud is a dark yellow mass that settles thickly on the ground like a heavy fog. It is the source of a Dusk's intelligence and the primary method of Dusk infection.