The Keepers are a bio-engineered, insectoid race found only on the Citadel. They are completely docile and harmless, and appear to exist for no other reason than to maintain the Citadel and its systems.
The Keepers are believed to have been created by the Protheans to serve as caretakers of the station, and have become essential to the Citadel's operation. Very little is known about them, as they do not communicate with other species, and it is against C-Sec regulations to interfere with Keeper activity.
Appearance
The Keepers have four pairs of limbs, with the two pairs of hindlimbs having three segments and the two pairs of forelimbs having only two segments. The forelimbs serve as arms and have appendages at each end that seem to be like hands. They stand on their two pairs of hind limbs. They also have a component attached to their back with an antenna sticking out. It is unknown what the use of this component is.
Biology
There is little known about the inner workings of the Keepers. If they are interrupted from their work for a prolonged amount of time, such as that which is need to properly study them, they proceed to make themselves self-destruct. Something in their bodies releases an acid or enzyme that almost immediately turns the Keeper into a puddle on the floor. It is not known how they reproduce; however, it is known that they do. No matter what kind of accident or violence numbers of Keepers befall, they still manage to keep a consistent population. No one knows where they come from. Their behavior, specifically that of maintaining the Citadel without being ordered to do so, has led to theories that they are actually constructs. There is also the possibility that they were once a race of creatures that were subjugated and consequently genetically modified by the Reapers in order to serve their needs.
Usage by the Reapers
The Keepers continuously maintain the Citadel in order to keep it an attractive center for races that have developed FTL technology. Once a certain level of technological knowledge is reached, Sovereign, a Reaper left behind to facilitate the continued reproduction of its race, sends a signal to all the Keepers that orders them to activate certain relays to call the rest of the Reapers. However, it seems as if the Keepers no longer respond to Sovereign's orders. Because of this, they are now seen as completely harmless and beneficial, as they will help repair and maintain the Citadel should anything happen.