They had great psionic powers and had specialists in time travel. They used these specialists and their own psi-powers to contact Jared Khan. The Charrl reproduced by biting their victims. The newly born offspring later hatched out of the host body. (PROSE: Birthright, AUDIO: Birthright)
The Charrl intended to use a Time Vector Generator to stabilise a temporal rift between Antýkhon and Earth of 1909 (known as the Great Divide) and travel back in time to conquer and live on Earth. They were foiled and Muldwych tricked them into thinking he had sent them to a new world when in fact they were in a replica of their home world contained inside of the 7th Doctor's TARDIS (PROSE: Birthright)
They ended up living inside the 7th Doctor's TARDIS for centuries, in the end they began regarding him as a god. Eventually a group made an expedition to the TARDIS console room (which they considered a great blasphemy) while the Seventh Doctor was absent during the events of Blood Heat.
During the time before the Doctor destroyed the timeline by time ramming his original TARDIS, the Charrl spent thirty generations trying to decipher the machine. By the time they had managed to pilot the TARDIS out of the tar pit the Doctor had lost it in, they were just in time to be time-rammed by the TARDIS he had acquired from his dead alternate self. However, instead of being destroyed they were transported upon the back of the Fortean Flicker (though they felt it was an example of the Doctor's all-powerful will) to Cheldon Bonniface. Upon arrival they attempted to clean it up and insisted on trying to throw flowers at the Doctor and asking him to lead them every time he even stuck his head round the door.
Due to their arrival and the fact that they had returned his original TARDIS to him, he invited a contingent of them to Bernice Summerfield's wedding. However, due to a misunderstanding of local customs, they tied up Jason Kane up and hung him upside down inside the TARDIS, preventing him from arriving at the weeding on time. They later left with Muldwych in the TARDIS the Doctor had been travelling in since the events of Blood Heat. (PROSE: Happy Endings)
Due to Irving Braxiatel's alteration of Bernice Summerfield's timeline, a second version of events was generated (both of which were experienced by Benny at different points in her life though she did not remember or realise during the events) in which the Charrl Queen was persuaded and assisted by Benny in moving the Charrl to a uninhabited planet in the Milky Way. (AUDIO: Birthright)