black fly

In the United States, a small, venomous, two-winged fly of the genus Simulium of several species, exceedingly abundant and troublesome in the northern forests; -- called also buffalo gnat. The larvæ are aquatic. It sucks the blood of birds as well as humans and other mammals. (Zool.)
A black plant louse, as the bean aphis (Aphis fabæ), which infests e. g. beans and sugar beets; -- called also bean aphid.