|Height||Varies with subtype|
|Weight||Varies with subtype|
|Notable Individuals||*Rachni Queen|
The Rachni are a insect-like species from the planet Suen that threatened Citadel space roughly two thousand years ago during the Rachni Wars. Intelligent and highly aggressive, the spacefaring Rachni were driven to expand and defend their territory. They were eventually defeated and completely eradicated by the Krogan, who had been uplifted by the Salarians for their combat prowess and physical resilience to directly confront the Rachni in the harsh environments of the Rachni worlds. The accidental discovery of the Rachni led to the Citadel races curbing their rapid expansion, in fear of being plunged into another galactic war.
- Rachni Worker - Workers are the smallest type of Rachni. They appear as small green enemies and their main attack is a suicide explosion that releases toxic damage over a wide radius.
- Rachni Soldier - Soldiers are slower, but much larger creatures than Rachni Workers, with thin tentacles ending in little pods. Soldiers are the main defenders of rachni held areas and can cause toxic damage with their spit.
- Rachni Brood Warrior - Brood Warriors are rachni who are much larger and stronger than normal Rachni Soldiers. They are male gendered Rachni and they have some biotic ability.
- Rachni Queen - Queens are the largest and most intelligent of the rachni. Queens lead the Rachni and provide guidance for the rest of their species.
The Rachni are a territorial race, determined to remain isolated from the rest of the galaxy. They normally inhabit extremely hazardous worlds, able to survive environments that would kill most sentient species. Should their territory be invaded on purpose or even by accident, they respond with swift and brutal force.
However, many make the mistake of underestimating the Rachni as mindless animals when in fact the Rachni are an extremely intelligent sentient species. The Rachni achieved space flight and a form of cryogenic suspension, developed weapons and carved out a huge swathe of galactic territory. Far from being treated as disposable resources of the hive, Rachni soldiers are carefully nurtured as part of the group.
The queens are the leaders of the Rachni hive mind. Their ways of perception, thinking and communications seem to be different from that of other races, and based upon a synesthetic perception of sound as both sound and color. Rachni communication is geared towards pheromones, and, as further proof of their intelligence, an organic quantum entanglement communicator - not, as so many believed, telepathy.
Rachni regard speech and thought as forms of music, as shown by the strange metaphors used when attempting to communicate, for example, "songs the color of oily shadow". The speech patterns used by them in such occasions are also unusual; "When we speak, one moves all". They refer to their manner of communication as "singing", which soothes and nurtures their young, and this appears to color their entire psychology - for example, the Rachni speak of death as "the great silence", and refer to their homeworld as the "singing planet". The Rachni ability to genetically share knowledge across generations makes queens a vast repository of information.