This is a four-part serial, first broadcast between 13th February - 20th March 1965. The serial was written by Bill Strutton, produced by Verity Lambert and directed by Richard Martin. The script editor was Dennis Spooner.
When the Tardis lands the Doctor, Vicki, Ian and Barbara find themselves caught between two warring alien races, the ant-like Zarbi and the moth-like Menoptera. They also encounter the Animus, a malign spider-like creature that is the story's villain. At the end of the last episode all is well: the Animus is dead, the Zarbi are vanquished and the exiled Menoptera, the planet's original inhabitants before the bad guys moved in, are free to come back home.
Let's start with the good points about this serial. It's clear that the makers were attempting to create a truly alien world inhabited by non-humanoid creatures with their own history and culture, and that kind of ambition is to be applauded.
Some of what the makers are doing here works surprisingly well. The use of lens filters and Vaseline is remarkably effective in creating the illusion of an atmosphere that is nothing like the earth's. The use of sound effects and the occasional fragment of almost atonal music, very different from the usual Doctor Who score, works well and is the one thing that I truly enjoyed about this serial.
The serial's biggest problem isn't that the aliens are clearly people in bug-suits. The aliens in 'The ark in space' are clearly people in bug-suits, and still many people like the serial.
The real problems are the pacing and the storytelling. The pacing is very, very slow, and there's little action. Much of the dialogue, like Vicki and Barbara discussing the virtues of Aspirin, seems pointless - doing nothing to either entertain or move the story forward. At the same time the story contains a number of different, seemingly under-developed story-lines that are easy to lose track of, leaving the viewer both bored and bewildered as a result.
It tried. It failed.