People often use “gnat” and “fly” interchangeably for small, winged insects, leading to widespread confusion about whether these common pests are distinct or the same. While both terms refer to flying insects, their usage in everyday conversation often differs from their scientific classifications. Understanding the distinctions between what are commonly called “gnats” and “flies” requires a closer look at their biological groupings and observable characteristics. This clarification helps in identifying and managing these insects more effectively.
Understanding the Scientific Classification
Scientifically, insects commonly referred to as “flies” belong to the order Diptera, a name derived from Greek meaning “two wings.” This order encompasses a vast array of insects, all characterized by having a single pair of functional wings, with their hind wings reduced to small, club-like structures called halteres that aid in balance during flight. This broad classification includes house flies, mosquitoes, midges, and even what are colloquially known as gnats.
Within the order Diptera, there are two primary suborders: Nematocera and Brachycera. Nematocera, meaning “thread-horns,” are typically slender insects with long, segmented antennae and often delicate bodies. This suborder includes mosquitoes, crane flies, and many of the insects commonly grouped as “gnats,” such as fungus gnats and drain flies. Conversely, Brachycera, or “short-horns,” generally comprise more robust flies with shorter, stouter antennae. Common examples within Brachycera include house flies and blow flies.
This scientific framework clarifies that all gnats are technically a type of fly, as they are all members of the order Diptera. However, the reverse is not true; not all flies are considered “gnats” in either scientific or common parlance. The informal term “gnat” thus refers to a diverse group of smaller, often more fragile-looking Dipterans, predominantly from the Nematocera suborder.
Key Differences in Common Usage
Beyond scientific classification, the common distinction between “gnats” and “flies” relates to observable characteristics, behaviors, and typical habitats. Insects commonly called “gnats” are generally smaller, typically ranging from 1.5 to 4 millimeters in length, and possess more delicate, slender bodies with long, thread-like antennae. These “gnats” are typically weak fliers and tend to make short, erratic flights.
For instance, fungus gnats (often dark gray or black) are frequently found hovering around houseplants, particularly those with moist soil, as their larvae feed on fungi and decaying organic matter. Drain flies, also known as moth flies, are another example, characterized by their small, fuzzy bodies and leaf-shaped wings, often seen in bathrooms or kitchens near drains where their larvae consume the organic film.
In contrast, insects commonly referred to as “flies” in a general sense, such as house flies or blow flies, are typically larger and possess more robust bodies, with shorter antennae. House flies, for example, are known for their strong, direct flight patterns and are frequently associated with decaying organic matter, animal waste, and food sources. Blow flies are recognized by their metallic blue, green, or black coloration and are attracted to carrion and dung. These observable differences in size, body shape, flight behavior, and preferred environments contribute to the everyday distinction people make between “gnats” and “flies.”