The group of insects known as true flies include house flies, fruit flies, horse flies, stable flies, black flies, and more than 100,000 additional fly species that have been documented worldwide. This massive number of species makes true flies one of the most species-rich insect groups, and they are distinguished from other airborne insects by their single set of wings, as opposed to the double set of wings that insects like butterflies, dragonflies, wasps and bees possess. True flies belong to the Diptera order of insects, and not all true flies resemble common house flies, but many are associated with the spread of disease. For example, mosquitoes and gnats are each made up of numerous species that are known biological disease vectors. Flies are also associated with the spread of disease, but unlike mosquitoes, the most common indoor and biting fly pests are mechanical disease vectors, not biological disease vectors.

Due to reproducing on decaying organic matter, such as excrement, animal carcasses, and rotting food, the exterior body of common fly pests are covered in dozens of pathogens. When fly pests enter a home, every surface that they make contact with becomes contaminated with these pathogens, and in some cases, fly-borne pathogens make contact with mucous membranes in the nose, ears, or mouth of humans, sometimes resulting in disease. For example, the common fly pest of homes that is frequently referred to as the face fly is known to dart into people’s eyes, fly up noses, and into mouths due to their attraction to tears and other human bodily secretions. Unfortunately, face flies are filthy and the pathogens on their body sometimes absorb into mucous membranes, which can lead to a variety of diseases, most commonly conjunctivitis, or “pink eye.” Face flies breed on cow manure, and they are nearly identical to common house flies, only slightly larger. Face flies can infest a home at just about any time of year in Louisiana, but they usually invade attics, wall voids and other concealed indoor areas in large numbers during the fall or early winter seasons in order to secure warm shelter for overwintering. When temperatures drop during the winter, face flies automatically enter into a state of inactivity until warm spring weather arrives. On unseasonably warm winter days, however, overwintering face flies emerge from their hiding spots in an effort to return outdoors. Unsurprisingly, these sudden mid-winter indoor fly swarms tend to surprise and annoy residents.

Have you ever encountered one or more flies within your home during the winter?