Similar in appearance. Both gnats and flies have many of the same features. They each have three body segments – the head, thorax and abdomen. They both also have wings and antennae. Most species of gnats are very small, measuring one-quarter of an inch in length or less. On the other hand, flies are usually considerably larger. The average house fly is one-quarter to one-third of an inch long and its larger cousin, the horsefly, can measure as much as one-half to 1 inch in length. Like most species of flies, gnats are either dark-colored or black.
From egg to adult. Is a gnat a baby fly? No, but they go through the same developmental stages. Each begins as an egg, then hatches into a larval – or worm-like – stage. Next, the larvae enter the pupal stage, which is often called a cocoon. From the pupal stage, they emerge as adults.
Point of confusion. It’s easy to understand why you might think flies are gnats. Baby flies are about the same size as an adult gnat. When they invade your home, both gnats and flies can be found in the same general areas. For example, fungus gnats feed and reproduce in locations high in moisture content where decaying organic matter is present. Fruit flies are found on or near fruits and vegetables that have ripened. This means that you’ll likely find both gnats and flies hovering around the same two rooms of your home – the kitchen and bathroom.