The Husnock were a species that was completely destroyed in 2366 by a Douwd who had assumed the Human identity of Kevin Uxbridge. Their physical appearance was unknown, but Uxbridge described them as "a species of hideous intelligence who knew only aggression and destruction." The Husnock population numbered to fifty billion at the time of their extinction.
In 2366, a Husnock warship attacked and destroyed a Federation colony at Delta Rana IV. Unknown to the Husnock, a Douwd was also living on the planet in the guise of Uxbridge. In a split-second of anguish over the Husnock attackers killing his wife, the normally pacifist Douwd destroyed every member of the Husnock race with its enormous powers. (TNG episode: "The Survivors")