Recent Outbreak of Biting Flies

By John Gordy, Fort Bend County Extension Agent-AG-NR

For the last couple of weeks there have been many local reports of and questions about biting “gnats”. Many of the reports indicate that the gnats are biting people during the day – particularly around the neck and head, and leaving persistently itchy swollen areas at the site of the bites. The actual culprits have been one or more species of black fly. Black fly species are small (5 mm or less) and have a characteristic “hump-back”, which is why they are also commonly called buffalo gnats. The flies are active during the day, and unlike mosquitoes, they are fast, strong fliers that can continue to be problematic even on very breezy days. Female flies have mouth parts modified to bite and feed on blood. They attack people as well as domestic animals, poultry and wildlife.

Most species of black fly larvae develop while attached to sub-merged rocks or logs in shallow moving waters of streams and rivers. However, there are some species that do well in sandy-bottomed streams and slow, muddy bodies of water. After the female lays eggs in the water, larval development can take any-where from two weeks to more than two months. Adult black flies, particularly females, can disperse great distances from their breeding habitats to feed. Along with the relatively warm winter we have experienced, rains farther north have provided ample freshwater coming down both the Brazos and San Bernard rivers, helping provide good conditions for large black fly populations. And while the black fly populations may soon decrease, it is possible that there will be another generation later in the year.

During periods of adult activity biting flies can become very annoying. Staying indoors is one option, but working outdoors may require dressing in long pants and long-sleeved shirt and wearing a cap and possibly a mesh veil. Insect repellents can be applied, particularly to the neck and head, but may not be very effective against these strong, fast flies. Additionally, you may have to try different repellents to find the one that works on the species near-est you. There is some research showing good efficacy of the active ingredient IR-3535 against some species of blackfly, deer flies and stable flies. Also, mixtures of DEET with other repellents like MGK 111, MGK 264, and MGK 326 appear to be better against blackflies than DEET alone. Some products that contain the above repellents include Avon Skin-so-soft Bug Guard, Coleman Skin Smart, Deep Woods Off, Sawyer picaridin repellent, and Cutter Backwoods. Additionally, some local re-ports indicate that herbal and essential oil based repellents work well, although there is no re-search to support it. Bites can be treated with over the counter insect bite remedies to help deaden the itching, but some people are very sensitive to the bites and may need to visit with their medical doctor.

For horses and livestock, individual animals may be stabled during the day when populations are abundant, but this practice is not possible for large herds. Fly repellents applied to the chest, belly and ears are somewhat effective but require daily application. Muslin or cotton bags fitted over horses’ ears may be used to prevent fly entry of those species attacking these areas, or white petroleum jelly inside the ears of horse will reduce bites. Additional options include dense smoke, repellents with permethrin, and ivermectin ear tags or pour-on and spray formulations.

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