Black Flies

Black flies (buffalo gnats) are once again starting to make their presence felt across the state. While we always seem to have some black flies every year, the last two years have seen higher than normal populations.

Black flies are small humpbacked flies that develop in running water (i.e. rivers, creeks, streams). While their numbers may be higher in areas adjacent to these breeding sites, the flies can be blown considerable distances from where they emerged. A number of different species of black flies occur in Iowa, with most species producing only one generation a year. Once a species has emerged, the adults can be expected to live for about 2-3 weeks.

The feeding habits of black flies are somewhat similar to mosquitoes in that only the females feed on blood. Like male mosquitoes, male black flies feed on nectar. However, unlike mosquitoes, black flies tend to bite in the middle of the day and are only active during daylight hours.

Black flies prefer to feed around the head area but will also feed around the wrists and ankles. As she feeds, the female black fly injects saliva into the skin to serve as an anticoagulant. This saliva is highly irritating and can lead to varying degrees of localized tissue swelling, particularly if the bite occurred around the eyes, lips, or ears. This localized swelling may last for 1-2 weeks and produce intense itching.

Large scale control of black flies is difficult. As a result, the best defense against these annoying pests is to use personal protection during the time periods when the adults are active. If possible, light colored clothing should be worn since black flies are more attracted to dark colors (i.e. blue, purple, brown, black). Tucking pant legs into the socks can also prevent black flies from feeding around the ankles. Insect repellents can provide some protection if they are applied to exposed body areas. However, when applying insect repellents to the head area, caution should be used to avoid getting these materials into the eyes or mouth.

Black flies can also be annoying to livestock and pets, particularly horses and dogs. A number of different products are available for direct application to horses that may provide some level of temporary relief. Similar products are also available for dogs. However, for dogs it may be easier to let them take shelter indoors during the day when black flies are most active.

This article originally appeared in the July 1, 1994 issue, p. 104.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 1, 1994. The information contained within may not be the most current and accurate depending on when it is accessed.