The Pantophagen were natives to the Time Vortex.
Pantophagen were powerful insectoids, capable of ripping through the metal cities of humanity in 4000, and devoured everything in sight. Despite Jalnik's hypothesis that the Pantophagen were sentient and talking to him, the Fourth Doctor quickly dismissed such a notion of them being sentient, as he would have been able to communicate with them if they were. (AUDIO: The Foe from the Future)
Little is known about the Pantophagen, before or after Jalnik discovered them during his primitive attempts of travelling through the Time Vortex. Believing they could be controlled, Jalnik and his conspirators attempted to set the Pantophagen loose on Earth a short while before the year 4000, but they proved to be far more dangerous than expected, with only two dozen or so Pantophagen devouring almost the entire planet. Some people were able to escape in spaceships, but after the Pantophagen virtually devoured every possible source of fuel, only one city was left, protected by a complex force field that could keep the Pantophagen out.
With no other alternative, Jalnik proposed that the surviving residents of the city travel back in time to escape the Pantophagen via his time corridor, but when he went back he was unaware that he had been contaminated by Pantophagen DNA through a small wound he had obtained during his research. As a result, the Pantophagen DNA mixed with Jalnik's system and turned him into the first Pantophagen hybrid, ravaged by hunger and capable of devouring a human in moments. He was able to hold onto his sanity for a time, but eventually suffered a mental breakdown, believing that the Pantophagen were speaking to him and wanted him to unleash them and a new species of hybrids like himself on Earth in the past.
When several were sucked into 1980s Earth, the Doctor used Jalnik's machine to control ghosts, to age them to death. Afterwards, he sealed the crack Jalnik was using to make his way to earth, preventing the Pantophagen from ever coming to Earth in the first place. (AUDIO: The Foe from the Future)