The Reetou are natives of Reetalia. They are large insect-like creatures, nearly 5 to 6 feet tall, who are invisible in our dimension. According to quantum physics, matter exists in both particles and waves. Because the Reetou waves are exactly 180° out of phase with Earth, their light and sound waves are undetectable in our dimension. However, they are able to function and operate objects in our phase to a certain degree.
Most of the Reetou were destroyed by the Goa'uld. In retaliation, Reetou rebels intend to defeat the Goa'uld through attrition by destroying all possible hosts. They work in small groups of five suicide infiltrators using powerful cross-phasal explosives. The Central Authority of the Reetou oppose the rebel plan, and they sent "Mother" and "Charlie" to warn Earth of the planned attacks against humans. The Reetou to whom Charlie referred as "Mother" had arrived through the stargate, undetected because of her invisibility, and had been observing the SGC for many weeks. Following SG-1's encounter with Tonané, she determined that O'Neill could be trusted, and she used the computer to open the gate and iris to allow Charlie, a young genetically engineered human of her creation, access to Earth to act as an intermediary and to deliver the warning.
A Goa'uld symbiote in a host or a Jaffa is sensitive to the presence of an invisible Reetou, reacting with extreme pain. A transphase eradication rod (TER) relies on the Reetou emissions to which the Goa'uld are sensitive, in order to make the Reetou visible in our phase, and to terminate them. SG-1 discovered a rebel base where thousands of Reetou had gathered. A single suicide squad eluded detection and returned with them through the gate, infiltrating the SGC. They were eliminated using TERs, but in the ensuing battle, Mother was killed by one of the rebels. Since the incident, a palm scanner has been installed in the control room to prevent Reetou from controlling the iris and returning through the gate.
Cross Reference: Alternate Dimension, Charlie, Invisibility, Palm Scanner, TER
Episode Reference: Show and Tell