Roots: The Doctor quotes from Proverbs 6 ('Look to the ant thou sluggard, observe her ways and be wise'), Nature films (the Zarbi migration and stampede). Tim Buckley's 'Starsailor', The Princess Bride ('insects of unusual size')
Intertextuality: Bill Strutton's Doctor Who and the Zarbi (Menoptran approximations of English, including 'Amnylsa' for Nyssa; 'Arbara' may be an adaptation of 'Paraba', the Menoptra's own attempt at Barbara). Menoptra worshipping towers of light and a crippled female Menoptra unable to fly also appeared in Scott Gray's comic strip The Naked Flame in the 1993 DWM Yearbook. A Zarbi queen (hence a hive society) was introduced in the 1965 Doctor Who Annual story The Lost Ones.
Dialogue Triumphs: "You have a new scent - and you are very ugly!"
Double Entendres: 'He knows something of the anatomy of your people [although] it's true he's not had a living sailor to study'
"It's become so hard to think. Look at me - look at my chest!"
Continuity: Natural desert hasn't formed in Vortis' Desolation in decades. The name of the Desolation comes from Vortis' Dark Times and refers to Pwadarauk, the creator of the soil and the darkness from Menoptran legend. According to the story the Universe and sky were created by The Light, but Pwadarauk created time and the ground so that things might wither and grow. Hruskin, the first Menoptera and grandmother of all others, told Pwadarauk of the world she imagined for her children, who would build beautiful temples for the Light and dance and weave songs. This world would be a paradise where no Menoptra would ever want or suffer. Pwadarauk asked Hruskin who would build the temples and raise the harvests work while the Menoptra were doing this; Hruskin suggested they have slaves, and so Pwadarauk created the Zarbi. Further legends of the Menoptra include those of the Exile, when Menoptra fled to Pictos. Acheron implicitly refers to the Optera of this time as 'pitiful things', a leftover story from the Exile Legends, suggesting that Menoptran society has not entirely moved on since the Doctor's last visit. The visible presence of Pictos [one of numerous moons, but the only satellite named] is a permanent reminder of the Exiles and provokes a backward, militant sentiment in the Menoptra of the cities.
The Menoptran city features tall spires - the Temples of Light. Menoptrans worship light itself and believe it to be sacred, some even believing there are gods within the light. Natural desert has been rare on this planet for ten generations, according to Hedyla, suggesting Menoptra have long lifespans (depending on one's interpretation of 'centuries'.) Menoptran homes have no ground-floor access; given the preferred means of travel for Menoptra (Acheron's laboratory is accessed via a window.)
Wingless Menoptra are quite rare, according to the Doctor. Menoptra usually build their nests in trees (with no ground-level access); their diet includes acidic substances; they digest their food more than once. Their society includes royal families, although it is implied that lineage is no guarantee of position (Hedyla could have been a queen due to her beauty.)
Zarbi live in hives which they probably build with a form of 'paper' (it is grey and ugly), as wasps do. They can burrow and habitually bury themselves below ground to ambush prey. Tame Zarbi may be ridden like horses, but must be saddled. Acheron implies that there may be several species (unless he is simply making a distinction between wild and domesticated or social Zarbi.)
The Doctor has always thought of Vortis as somewhere he could relax. He carries a form of light in his pocket which he uses to distract the Zarbi.
Future History: Humanity for a time opts to colonise space by sending out 'seed ships' to locate worlds where humans can't yet live. On landing the two specimens (male and female in this instance) adapt to local conditions and, once their biological programming is initiated, merge into one creature - an enormous cocoon - from which hundreds of children biologically adapted to the local environment emerge. Their normal life cycle appears to be mere days.
Q.v. 'The Elder Gods'
Untelevised Adventures: The Doctor is cagey about his knowledge of Pictos' [and other moons'] appearance, suggesting he may have been involved in Vortis' future at other times in its past (though see Intertextuality)
Links: The Web Planet.
Location: Vortis, 'hundreds of years' after the events of The Web Planet and some way into Earth's future. The Doctor deduces much the same through the existence of the moon Pictos, which began to orbit Vortis shortly before his first incarnation's arrival.
Bottom Line: Straightforward, and an ideal candidate for a subscriber-bonus story. Kudos to O'Mahoney for managing to fit so much of Vortis' accrued continuity into the story, even though the supporting cast seems particularly small with only four other speaking roles.