The term “gnat” is commonly used to describe various small, flying insects. While many gnats are simply annoying, they can cause sickness, depending heavily on the specific species involved. Health concerns arise from two main sources: the direct physical consequences of a bite and the indirect transfer of pathogens from contaminated sources to humans.
Distinguishing Biting and Non-Biting Gnat Species
The term “gnat” is a catch-all name for multiple families of small flies, including biting midges, black flies, fungus gnats, and eye gnats. These groups fall into two categories: those that bite for a blood meal and those that feed on organic matter or secretions. Biting species, such as biting midges, also known as “no-see-ums,” and black flies, possess specialized mouthparts to cut the skin and feed on blood, which is necessary for the female to produce eggs. Non-biting species like fungus gnats and drain flies primarily cause nuisance or contamination. Fungus gnats are attracted to moist soil and decaying plant matter, while drain flies breed in organic sludge. Eye gnats persistently swarm around the eyes and open wounds to lap up secretions, a behavior that carries distinct health risks.
Immediate Health Risks from Gnat Bites
The immediate health risk from biting gnats comes from the physical reaction to the insect’s saliva. Biting midges and black flies inject anticoagulant compounds, and the body’s immune response causes localized irritation. Symptoms typically include redness, swelling, intense itching, and the formation of a small, raised welt at the site of contact.
The most common complication following a bite is a secondary bacterial infection. Excessive scratching breaks the skin barrier, allowing bacteria from the skin or under the fingernails to enter the wound. Signs of infection include persistent redness, increased swelling, warmth, or pus. Rarely, susceptible individuals can experience a severe systemic allergic reaction, which may involve hives, extended swelling, or anaphylaxis requiring immediate medical attention.
The Role of Gnats in Spreading Pathogens
Gnats contribute to sickness through the mechanical transmission of pathogens. Non-biting gnats, especially those attracted to unsanitary conditions, transfer infectious agents from one surface to another. They feed or rest on decaying organic matter, feces, or infected fluids, picking up bacteria, viruses, or mold spores on their bodies.
Eye gnats (Liohippelates) are problematic because they are strongly attracted to the moisture and secretions around the eyes and open wounds. By moving from a contaminated source to a person’s eye, they can transfer bacteria responsible for acute bacterial conjunctivitis (“pink eye”). Gnats that land on food preparation surfaces after contacting garbage or excrement can also transfer bacteria like Salmonella or E. coli, posing a risk of gastrointestinal illness.
Controlling Gnat Populations to Minimize Health Concerns
Minimizing health concerns begins with eliminating the sources that attract gnats. For biting species that breed in water, removing sources of stagnant water (e.g., poorly drained areas, clogged gutters, or old containers) reduces egg-laying sites. Personal protection, including using insect repellents containing DEET and wearing protective clothing, helps prevent direct contact.
Controlling Non-Biting Species
Control for non-biting gnats focuses on sanitation and moisture management. Fungus gnats thrive in overly moist soil, so allowing the top layer of potting mix to dry out prevents reproduction in houseplants. Drain flies are controlled by regularly cleaning plumbing fixtures to remove the organic film where their larvae develop. Overall cleanliness, such as securely storing food and using fine-mesh screens, prevents indoor access and reduces the availability of materials that attract contaminating species.