The Krillitanes were a race that could take physical features from races they conquered. They would "cherry-pick" the best bits from the people they destroyed.
The Krillitanes were able to take the abilities from other species, giving them new appearances and qualities. Unable to shape-shift, they could create morphic illusions, keeping them cloaked in human form. Their wings were capable of lifting heavy things.
In 1140, the Krillitanes were in the initial stages of their bat-like forms, having only recently conquered Bessan and, as such, had hooked tails and longer necks. This gave them the impression of the devil to the human natives of Earth at the time. The Krillitane oil had become toxic to them by this point because of continued overuse and physiological alterations. (PROSE: The Krillitane Storm)
In 2007, the Krillitanes had become more human-like, with shorter necks and smaller tails. They had various shades of skin ranging from pinkish to charcoal grey, sharp claws and a flattened, fanged face. They slept upside down like bats and had very sensitive hearing. The Krillitanes were carnivorous and would eat other sentient creatures, but they would also eat rats. (TV: School Reunion)
Krillitanes also produced Krillitane oil. (TV: School Reunion, PROSE: The Krillitane Storm) As an unfortunate side-effect from their sensitive ears, they were highly susceptible to high-pitched noises, such as a fire alarm. They were also very strong, as Lassar was able to punch through a wall and rip out the power cable to the fire alarm when cloaked as a human. (TV: School Reunion)
Krillitanes had spaceships and were capable of creating deadlock seals. (TV: School Reunion) As the Tenth Doctor observed, they seemed to change the design of battlecruisers every time they amalgamated a new race. (COMIC: Fugitive)
The Tenth Doctor reacted in fear when he discovered the oil used on Deffry Vale High School's chips was Krillitane oil. When Rose asked if the Krillitanes were bad, the Doctor responded, "Think how bad things could possibly be and add another suitcase full of bad." (TV: School Reunion)
In 1140, Lozla Nataniel Henk attempted to breed Krillitanes in Worcester, but was defeated by the Tenth Doctor. By using their own oil against them, Henk attempted to create a huge, mutated Super Krillitane that he could sell to the highest bidder as a weapon. However, the creature was killed when Captain Darke threw a vial of Krillitane oil into its mouth as it was rampaging around the city of Worcester. (PROSE: The Krillitane Storm)
In 2007, a group of 13 Krillitanes led by Brother Lassar landed in Deffry Vale High School in London. They took over Deffry Vale High School, disguising themselves as the teachers. Using Krillitane oil and an advanced computer network, they were using the brains and imagination of the students as a type of computer in order to work out the Skasis Paradigm. Mickey Smith deactivated the computer network and evacuated the students the Krillitanes were using, while K9 Mark III sacrificed himself, killing the Krillitanes when he blew up a vat of Krillitane oil with his laser. (TV: School Reunion)
In 2010, Krillitanes tried again to improve humans' brains with their oil employed in the Brainy Crisps; without knowing, the enhanced consumers of crisps helped design a new form for their species. Eventually the plan was foiled by the Tenth Doctor and Henry. (PROSE: Code of the Krillitanes)
Behind the scenes
- Krillitanes were originally called Krillians, until a check revealed that this was the name of a real computer company. (DWDVDF 7)
- Russell T Davies' original concept for the Shadow Proclamation scene in The Stolen Earth included an appearance by several swooping Krillitanes, but his plans to feature a "rogues gallery" of alien races in the scene fell through; ultimately the Judoon were the only returning race featured.
- Krillitanes are included in the Micro-Universe Series.
- On the Series 2 outtakes reel, there are "bloopers" featuring animated creatures from the series getting into antics, such as the Krillitanes and the werewolf, done just for fun.