How a Mosquito Operates is a 1912 silent animated film by American cartoonist Winsor McCay. The six-minute short depicts a giant mosquito tormenting a sleeping man. The film is one of the earliest works of animation, and its technical quality is considered far ahead of its time. It is also known under the titles The Story of a Mosquito and Winsor McCay and his Jersey Skeeters.

McCay had a reputation for his proficient drawing skills, best remembered in the elaborate cartooning of the children's comic strip Little Nemo in Slumberland he began in 1905. He delved into the emerging art of animation with the film Little Nemo (1911), and followed its success by adapting an episode of his comic strip Dream of the Rarebit Fiend into How a Mosquito Operates. McCay gave the film a more coherent story and more developed characterization than in the Nemo film, with naturalistic timing, motion, and weight in the animation.

How a Mosquito Operates had an enthusiastic reception when McCay first showed it as part of his vaudeville act. He further developed the character animation he introduced in Mosquito with his best-known animated work, Gertie the Dinosaur (1914).