The term “gnat” commonly refers to various small, flying insects, but only specific types bite humans. These biting insects can cause irritation and discomfort. This article explores the biological reasons certain gnats bite humans.
Identifying the Biting Insects
The insects most often called “gnats” that bite humans are typically biting midges, black flies, and sand flies. Biting midges, known as “no-see-ums” due to their minuscule size (1-3 mm), are small, gray, two-winged insects found worldwide near wet environments. Black flies, also called buffalo gnats, are slightly larger (1-5 mm) with a stout, humpbacked body and broad wings, found near flowing water. Sand flies are small, brownish or gray insects, about 1/8 inch long, distinguished by hairy bodies and V-shaped wings held upright. They are common in tropical and subtropical regions.
The Purpose Behind the Bite
Biting is exclusively carried out by female gnats for reproduction. Female gnats require a blood meal to obtain protein for their eggs to develop properly. Male gnats do not bite humans; they feed on plant nectar or other sugar sources for energy. This need for blood is a fundamental part of their life cycle, ensuring the successful maturation of their offspring. Without a sufficient blood meal, a female gnat may lay fewer eggs or none at all.
How Biting Gnats Find Their Targets
Biting gnats employ several sensory mechanisms to locate human hosts. Carbon dioxide, exhaled by humans, is a primary attractant that gnats detect from a distance. Body heat is another significant cue, with gnats possessing specialized receptors to sense temperature differences. They are also drawn to moisture, such as sweat and tears, and certain chemical compounds or odors on human skin. These signals, combined with heat and carbon dioxide, help gnats pinpoint their targets.
Common Reactions to Gnat Bites
When a biting gnat feeds, it uses scissor-like mouthparts to cut the skin and draw blood, injecting saliva into the bite site. This saliva contains anticoagulants, which prevent the blood from clotting. The human body’s immune system recognizes these foreign proteins in the saliva, triggering a localized inflammatory response. Common symptoms at the bite site include itching, redness, and swelling, often appearing as small welts or papules. The intensity of these reactions can vary among individuals based on their immune sensitivity to the gnat’s saliva.