The snow gnats are white gnats found in the Mortmain Mountains and other frigid, high-altitude areas. They attack in well-defined, wind-based swarms and produce a mildly poisonous venom which can prove damaging in large doses. Snicket describes their aggressive behavior as "for no reason whatsoever." The most effective means of repellent is fire, and "even the smell of smoke can keep a whole swarm at bay." In an attempt to coin a V.F.D. name for them, Violet refers to the gnats as "violent frozen dragonflies", although gnats are members of the suborder Nematocera, while dragonflies are of the only distantly related suborder Epiprocta. Snow gnats are the main element of the stricken salmon's diet.
Jacques Snicket apparently suffered an encounter with the gnats so devastating he "had nightmares about it for weeks." Snicket describes how an "associate" of his fell over a cliff in the Mortmain Mountains while pursued by the gnats. Within the series, the Baudelaires are attacked by snow gnats while lost in the Mortmain Mountains. The gnats are described as forming an arrow shape and creating a vortex around the children.