This serial was wiped by the BBC and no copy of it is known to exist.
The Macra were originally giant insects. It was thought that they would be too similar to The Zarbi from The Web Planet. However, some dialogue comparing them to insects remains.
In the original script, the Pilot was named the Prime Minister.
Working titles for this serial include: "The Spidermen", "The Insect-Men" and "The Macras".