The Zarbi resembled giant ants. Some Zarbi moved on two powerful human-like legs, (TV: The Web Planet) while others, like the ones in the London Underground, moved on six legs like ants on Earth. (COMIC: Unnatural Selection) They communicated by screeching and rubbing their legs together. (TV: The Web Planet) Much like bees, Zarbi also communicated by dancing. (COMIC: The Macrobe Menace) They were naturally simple-minded creatures, no smarter than cattle. They had no individual motives. (TV: The Web Planet)
Socially, they were similar to the ants of Earth. They lived in massive nests with millions of members. There was also a similar caste system, with powerful warrior Zarbi, common workers and giant, bloated queens. They were born as larva, which were little more than grey blobs. (PROSE: The Lair of Zarbi Supremo)
The Zarbi were used by the Menoptera as cattle until there arose a queen which declared war against them, forcing them to flee to the moons. An advance scouting party sent to spy on the Zarbi also encountered Atlanteans and the First Doctor. When the Atlanteans escorted the Doctor back to his TARDIS, a battle between the Zarbi and the Menoptera was being waged nearby. (PROSE: The Lost Ones)
The Animus arrived on Vortis and took control of Zarbi, forcing them to fight their former masters. They reverted to their original nature after the First Doctor, Ian Chesterton, Barbara Wright and Vicki defeated the Animus. (TV: The Web Planet)
The Animus was able to reform and with help from another enemy of the Doctor teleported to the London Underground, where the Zarbi attacked the First Doctor, Ian, Barbara and Vicki. The Animus was defeated when Ian hit it with a train, and all of the Zarbi were teleported home. (COMIC: Unnatural Selection)
The Menoptera and the Zarbi worked peacefully together for many years, until the Zarbi apparently developed flight and deadly stingers, which they used to attack Menoptera. The First Doctor, John and Gillian arrived and, investigating, discovered that the flying Zarbi were actually Zarbi-shaped vehicles piloted by Skirkons, who had come to Vortis for its supplies of Galvinium X, and had enslaved the real Zarbi to oversee their Menopteran slaves. The Doctor and his grandchildren freed the Menoptera and defeated the Skirkons, who died when their base was destroyed. (COMIC: On the Web Planet)
Many years later, the relationship between the Menoptera and the Zarbi had patched up, with both forces helping the other. However, a strange mutation led to the creation of the Zarbi Supremo, a twenty-foot tall Zarbi who took control of the other Zarbi. It was able to devise means to move Vortis, turning it into a rogue planet.
Over several generations, Vortis left the Isop Galaxy and found itself near Jupiter. The Zarbi Supremo planned to take over Earth for its resources. The Menoptera had tried to deal with this, building up weaponry and infiltrating the hives, but the agents were captured or killed. At the same time, the Earth ship Solar Queen came to investigate the rogue planet, but when the scientists went to investigate they were also captured. They were able to send a message out, which attracted the First Doctor. With the help of Gordon Hamilton, he was able to free the scientists, who killed the Zarbi Supremo and released the Zarbi from their subjugation. With that, the scientists were returned to their ship and the Menoptera left the solar system for their own galaxy. (PROSE: The Lair of Zarbi Supremo)