By Muriel Bristol | May 11, 2018
The very last vestiges of packed snow situated in shady spots disappeared by Mayday. The Spring warmth that dissipated the snow also brought out the black flies. They are typically a nuisance between about Mother’s Day and Father’s Day. I try to remember what my grandfather always said: we need the black flies, as they are food for the fish and birds.
According to a UNH Cooperative Extension fact sheet, New Hampshire is home to 40 species of black flies, of which only 4 or 5 are considered to be either annoying or “significant” human biters. Only the female bites and most species feed on birds or other animals.
Black flies breed in running water. Females lay their eggs on stream vegetation or the water surface. When the larvae hatch (as water temperatures reach the 40-to-50 degree range), they attach themselves to rocks, leaves, grass or other submerged objects. The larvae pupate underwater and emerging adults rise to the surface to fly in Spring or early Summer. They mate near their hatching site and female seeks a blood meal (you) before laying eggs to begin the cycle again.
Only two species of black flies in New Hampshire consistently and abundantly bite humans. These are Prosimulium mixtum and Simulium venustum. Simulium venustum, the so-called “white-stockinged” black fly emerges in early to mid-May in southern New Hampshire and remains a pest until the end of May. In the north, it emerges in late May to early June and can remain abundant until the end of June in some areas and even into July in higher mountain localities (UNH/CE, 2009).
Light clothing colors such as orange, yellow and light blue are less attractive to black flies than dark green, brown and red. They are drawn also to perfumes and aftershaves.
The same remedies used for mosquitoes work also on black flies, although less effectively. The Centers for Disease Control recommend DEET, Picaridin, IR3535, and Oil of Lemon Eucalyptus for use in repelling biting anthropods, including black flies.
Years ago, Ole Time Woodsman Fly Dope was considered quite an effective repellent (although it had a very strong smell) and it was widely available in sporting goods stores. Johnson’s Baby Oil was said to be effective also.
Black flies are active only during the day. They do not bite at night. Depending on weather, black flies tend to be more active at certain times of day. Activity peaks tend to occur around 9:00 to 11:00 AM and again from 4:00 to 7:00 in the late afternoon and early evening, or until the sun falls below the horizon. They tend to be most active on humid, cloudy days and just before storms. If possible, avoid activity during times when black flies are most active. Early morning, midday and late evenings are the best times to work outside (UNH/CE, 2009).
The University of Maine Cooperative Extension has been quoted as saying that
Generally black fly bites cause some itching and minor swelling from the first few bites of the season, following which an immunity develops, with subsequent reduced reactions. Nonetheless, even individuals who have lived all their lives in black fly country and are exposed every season, can have greater effects if they get an unusually high number of bites on their first exposure of the season, or have some significant change in their physical condition or medical status.
See also Hot Water for Itchy Bug Bites
Ole Time Woodsman. (n.d.). [Home Page] Retrieved from https://oletimewoodsman.com/
University of Maine Cooperative Extension. (2012). Insect Repellents [Fact Sheet]. Retrieved from https://extension.umaine.edu/ipm/ipddl/publications/5108e/
University of New Hampshire Cooperative Extension. (2009, July 1). Black Flies [Fact Sheet]. Retrieved from https://extension.unh.edu/resource/black-flies-fact-sheet
Walmart. (2018). Coleman Mosquito Head Net. Retrieved from https://www.walmart.com/ip/Coleman-Mosquito-Head-Net/13848609