The only evidence for the existence of the Husnock race is the word of the Douwd, who claimed to have exterminated all of them after his human wife was killed in their attack on Rana IV. He claimed to have completely wiped them out -- all 50 billion of them -- and no remains of their civilization have ever appeared. It is entirely possible that they are a made-up scape-goat.
The Douwd described the Husnock as "a race of hideous intelligence, who new only aggression and destruction." Even assuming they actually existed, this is a questionable description, as it seems unlikely that a race with such behavior could build a thriving civilization.
The Douwd created an illusionary Husnock starship to attack the Enterprise-D when it came to investigate a distress signal from the Rana IV colony. This ship had five times the mass of the Enterprise and carried "enough firepower to pulverize a planet". The ship was quoted as firing "jacketed streams of positrons and anti-protons" with an equivalent firepower of up to 400 GigaWatts. Three shots brought down the shields of the USS Enterprise, and the third volley caused enough internal damage to force the Enterprise to retreat. If the Husnock were real, and this ship was representative of their capabilities, they would have been one of the most powerful and dangerous civilizations in the Alpha Quadrant.