Many dozens of insect species belonging to the family Tabididae have been documented as inhabiting Maine, several of which are known for inflicting painful bites on human skin. Tabididae species are commonly referred to as “horse flies” and “deer flies,” and just like house flies, Tabanidae flies are “true flies” in the order Diptera. Horse flies generally refer to species belonging to the genus Tabanus, while deer flies refer to species in the genus Chrysops, but the family Tabanidae also includes a small number of species in the genera Atylotus, diachlora and Hybomitra. In Maine, a little more than 40 biting fly species from the genera Tabanus, Chrysops and Hybomitra are known for attacking humans in large numbers in order to obtain blood meals. Two well known biting fly pest species known as striped horse flies (T. lineola) and greenhead flies (T. nigrovittatus) are particularly aggressive biters that emerge in Maine at the beginning of July.

Both male and female adult biting fly species feed on plant fluids, but the females suck blood from humans and animals in order to obtain the nutrients they need to lay viable eggs. Horse flies and deer flies prefer to feed on the blood of livestock animals, but they also favor human blood, which meets the female’s reproductive needs. Horse and deer fly adults possess mouthparts that consist of scissor-like structures that tear into skin, and their saliva contains anticoagulant proteins that enhance blood flow. In addition to inflicting painful bites, biting flies are very fast flyers, and it is not uncommon for large groups of people to go running for shelter to escape menacing swarms.

Biting flies are attracted to movement and dark colors, and they can detect the breath of humans from faraway distances. Because of this, people spending time outdoors during the summer in the northeast are advised to avoid wearing dark colored clothing, and while repellents containing DEET will not prevent biting flies from landing on humans, they may be somewhat effective at preventing bites. However, anecdotal reports suggest that repellents of all kinds are largely ineffective against biting fly pests. Greenhead flies occur in every coastal county in Maine, and they breed in salt marshes before emerging to terrorize residents of coastal communities. The striped horse fly breeds in inland freshwater sources, but they are occasionally collected from coastal marshes. This species is prevalent in Kennebec, Cumberland, York, and Lincoln Counties.

Have you ever run for shelter in an effort to escape a swarm of biting flies?