New Hampshire Glossary: Black Fly (They're Back!)

Black flies are tiny annoying insects that occur in large numbers in the spring and early summer months in New Hampshire (and other northern states), especially in rural areas.  They breed in our moving water, such as rivers, creeks and streams.

In New Hampshire more than 40 species of black fly call us home (be happy, Alaska has counted more than 100 different species). Only two of the New Hampshire species usually bite human beings–Prosimulium mixtum, and Simulium venustum. Unfortunately, between the two species, they make most of the summer months uncomfortable–the first from May to June or July,while the second during August and September.

Some folks believe that the New Hampshire variety of black flies are big enough to “saddle up and ride,” when in fact at adulthood they measure only about 1/6th of an inch long.

Black flies are active during the day. Their tendency to bite increases as sunset approaches, so dusk is the worst time to be outside. Black flies do not attack at night, and so to best avoid them, do not go outside during the daytime.

Black flies find dark colors (and clothing) more attractive that pale ones, and they prefer blue, black, brown and purple to white or yellow.

To learn more, select one or more of the links below.



Black Flies (UNH Cooperative)

-Black Flies & Mosquitoes, What Good Are They? (PDF)-

-All you Wanted To Know about Black Flies, and More-

-Some Questions and Answers About Black Flies in Maine

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