Only a small number of males were kept alive for reproduction, the rest being killed to preserve resources. Drahvin females were attractive, ruthless and aggressive. In the military, the soldiers were all artificially created, while the officers were naturally born.
The officers thus looked down on the soldiers, and did not regard them as "proper" life forms. Most soldiers meekly accepted this class distinction.
One Drahvin ship battled a Rill ship and the two crash-landed on an uninhabited, doomed planet. The Drahvin leader, Maaga, tried to trick, then force, the Doctor into helping them destroy the Rills and escape the planet, but failed. The Drahvins died when the planet exploded.
They attempted to invade Earth at some point prior to 1997.