Kiseibya

The Kiseibya were parasitic creatures bred by Professor Shimura at the research facility Roarke 279 on Bliss. The Professor bred them as a weapon against the Daleks, combining the DNA of the Pirhanalocusts (dangerous flesh-eating insects) with silkworms to create metal-eating parasites, eating meat in their larval stage and laying their eggs in their 'food'. The Professor reasoned that this would allow them to 'eat' the Dalek casing and lay their eggs in the Dalek mutant. Shimura had intended to keep the Kiseibya contained until he could breed them to a point where they would be unable to consume human flesh, but the arrival of a Dalek attack force in the system apparently forced him to release the Kiseibya early. They fed and bred in his fellow scientists. He reasoned the scientists would die anyway when the Daleks arrived and their deaths would accomplish something this way.

Although the Kiseibya proved effective against the Daleks (although vulnerable to most weapons, the speed of the Kisaabya’s gestation and reproduction, coupled with their ferocity in attack, helped to counter that weakness), the Seventh Doctor was unnerved by the similarities between Shimura and Davros’s research. Both had created a new race to "save" theirs from a prolonged war. Both were unprepared for their creations’ unwillingness to obey them. Shimura protested that his creations would stop the Daleks and save mankind, but the fact that the name "Kiseibya" means "parasitic saviour" suggested to the Doctor that Shimura knew what he was doing was ethically conflicted from the beginning. As the Daleks invaded the facility, killing the Valkyrie unit, the Kiseibya attacked the Daleks, tearing through a Dalek platoon, leaving the Black Dalek - now infested with Kiseibya eggs - as the only survivor when the Doctor arrived.

Recognising the horror of the Kiseibya, he realised that he actually felt sorry for the Black Dalek. With the Valkyrie unit now dead, the Doctor, having confirmed that the Kiseibya’s Piranhalocust nature would drive them to procreate so they could survive on Bliss, programmed the Black Dalek’s damaged casing to self-destruct - with the Dalek’s permission - while positioning it beside the base’s power cells. The remaining Daleks on planet ordered their ship to depart to prevent the Kiseibya spreading before exterminating themselves. The Doctor departed the base before the Black Dalek exploded, destroying the facility and the Kiseibya; the very atrocity that history recorded would take place. (BFA: Enemy of the Daleks)