The Husnock were an intelligent species and civilization. They were very aggressive and conquered other worlds. They were made extinct in 2366, when they numbered around 50 billion. The Husnock had been described as "a species of hideous intelligence, who knew only aggression and destruction." Their physical appearance was unknown.

In 2366, a Husnock warship attacked and destroyed the Rana IV colony. Unknown to the Husnock, an energy lifeform known as a Douwd was also living on the planet, in the guise of Kevin Uxbridge. Despite having seen illusions created by the Douwd which tricked them, they still succeeded in destroying the colony. In a split-second of bereaved anguish over the Husnock attackers killing his wife Rishon, the normally pacifist Douwd lashed out with its enormous powers to annihilate not only the attacking ship, but the entire Husnock race. (TNG: "The Survivors")

"The Survivors" remains the Husnock's sole "appearance" in Star Trek. No Husnock were seen in the episode and the Delta Rana warship may not be a real recreation of a Husnock vessel, given Kevin's power to create "disguises and false surroundings."
According to the novel Fortune of War, the Husnock were a non-humanoid race with dark blue blood and seven tentacles, four of which were used for locomotion. Their government was called the Husnock Star Kingdom.
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