Adult Slitheen are 2.4 metres (8 ft) tall with overweight but muscular builds, long forearms, powerful sharp claws, and baby-like faces.

The Slitheen disguise themselves by crawling into the skins of their victims, using compression fields created by a collar worn around their necks to squeeze their huge size into a smaller space.

The acidity dissolves the skin, causing the internal organs to drop into the liquid while the condemned is still alive, reducing them to "soup" in a slow and painful death.

[3] Davies was impressed by Annette Badland's performance as Blon Fel-Fotch Pasameer-Day Slitheen during the production of "Aliens of London" and "World War Three," and asked her if she would be willing to return to the programme for the future.

[5] In an early draft of "The Gift," the Slitheen had a bigger role, aiding the human characters in stopping the spread of "Yorrum Grass" (an earlier version of the "Rakweed" used in the final episode) before betraying them to the Blathereen.

[6] When they first appeared in "Aliens of London" (set in 2006), the Pasameer-Day branch of the Slitheen had been in Great Britain for some time, having infiltrated various levels of British society, from community leaders and military personnel to mid-level politicians and government officials.

Their intent was to instigate World War III and sell the radioactive remains of Earth to a depressed galactic economy as fuel for interstellar spacecraft.

Before the Slitheen could receive the launch codes, the Ninth Doctor arranged for a Harpoon missile to demolish 10 Downing Street, ending the scheme and killing all but one of them who managed to escape through an emergency teleport.

[7] Jocrassa's sister Blon Fel-Fotch Pasameer-Day Slitheen, who had assumed the identity of Margaret Blaine of MI5, survived and reappeared in the episode "Boom Town".

[10] Another Slitheen (who was either a child or a short adult) appeared in the 2009 special "From Raxacoricofallapatorius with Love", masquerading as a galactic diplomat in an attempt to steal Sarah Jane's robot dog K-9.

In the Series 3 finale of The Sarah Jane Adventures, The Gift, a pair of Slitheen-Blathereen from an intermarried line of the two families attempted to overrun Earth with Rakweed, a plant native to Raxacoricofallapatorius and used as an addictive vegetable.

[12] In "Dalek", a stuffed Raxacoricofallapatorian arm was among a collection of alien artefacts owned by American billionaire Henry van Statten in the year 2012.

Rose later mentioned the Slitheen Parliament of Raxacoricofallapatorius in "The Christmas Invasion" (though her impromptu speech was a pastiche of phrases she had picked up on her travels with the Doctor).

In the 2006 series episode "Love & Monsters", an alien called the Abzorbaloff, whose natural form is similar to that of the Slitheen, claims to be from Raxacoricofallapatorius's twin planet Clom.

A Slitheen appears briefly in the Tenth Doctor novel The Nightmare of Black Island by Mike Tucker, created from Rose's memories, along with a Dalek and the Nestene Consciousness.

In the Torchwood episode "Reset", a newspaper clipping of Blon posing as Margaret Blaine, previously seen in "Boom Town", can be seen as Martha Jones enters the Hub.

The Doctor Who website" features a segment called Captain Jack's Monster Files, narrated by John Barrowman, which provides information about alien species.

It speaks volumes that the costumes were often reused in the more child-oriented The Sarah Jane Adventures and have been left to rot since Steven Moffat took over Doctor Who.