Plural of blackfly; small biting insects that swarm near water, causing painful welts and sometimes transmitting diseases.
Simple pluralization of 'blackfly' (from 'black' and 'fly'), referring to the dark-colored pest insect.
Black flies are so small and numerous they form actual clouds—in some northern regions, they're considered worse than mosquitoes, and a single bite can cause an itchy welt that lasts days.
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