The Brain Spawn are a race of big, flying brains who travel from planet to planet and destroy all sapient thought, which they hate, eventually eliminating the planet in question.
They came into being milliseconds after the Medium-Sized Bang and have been at war with the Nibblonians ever since. The Brain Spawn's ultimate goal is to gather all the knowledge in the universe, ultimately leading them to construct the Infosphere. Once all information in the known universe is collected, the Brain Spawn intended to destroy the universe, to ensure that no new information would be created, although this was stopped by the Planet Express crew.
The Brain Spawn cannot see, and can only detect the Delta Brain Waves of a sapient being. Their chief combat ability is to send out a stupefication field that eradicates all intelligence within the blast radius; presumably the field attacks the Delta Brain Wave itself. This makes Philip J. Fry the ultimate champion against the Brain Spawn, as he lacks the Delta Brain Wave and therefore can neither be seen nor fought by them. The Brain Spawn hate conscious thought for several reasons, among which is the fact that thought by others other than themselves hurts them. This is one of their few weaknesses.
The Brain Spawn have three apparent classes:
- Small Brains: Foot soldiers of a sort, which exist in huge numbers. Capable of stupefying an entire planet in a matter of hours.
- Big Brains: A sort of "General", more intelligent, capable of speech, and can trap beings in fictional worlds created from books.
- Huge Brain: Only one ever seen, capable of firing a beam that can instantly kill large species, such as dinosaurs.
- Flying ability.
- Stupefaction Field.
- Interstellar travel.
- Survival in most environments, including the vacuum of space.