A group of gnats is commonly called a Cloud. Other collective nouns you may see include Horde and Swarm.
A collective noun for a group of gnats is a cloud. These tiny insects, with numerous individuals fluttering and darting through the air in swarms, create a visual spectacle that resembles a hazy cloud. As gnats congregate in large numbers for breeding or feeding purposes, the term "cloud" effectively captures their characteristic behavior. Furthermore, this collective noun metaphorically conveys the ethereal and transient nature of gnats' presence, akin to the evanescent forms of clouds moving across the sky. Overall, referring to a group of gnats as a cloud encapsulates the captivating sight they create and emphasizes their temporary presence in a poetic and descriptive manner.
Known collective nouns for Gnats include: