|Appearance:||Survival of the Fittest|
They were communal, with various members organised into different functions: workers, watchers, warriors, healers and male drones. Like many insect species, over all of them was a fertile queen, or "Authority". The Vrill did not have individual names but the Doctor gives the two worker Vrill the names "Rose" and "Lilly" due to their smells and the newly hatched warrior Vrill the name "Butterfly" due to its magnificent wings.
At the centre of the colony was a hatching yard where the Authority laid thousands of eggs in a geothermal pool of hormonal fluids which cured the eggs and the resulting pupae became warriors, workers or male drones. Without fertilisation, the eggs hatched in their default warrior state. It was possible to create a new Authority by releasing certain nutrients into an egg but only an existing Authority possessed this ability.
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