What does blackfly mean?
Blackfly is a noun with two main meanings that vary by region. In British gardening, it denotes any of several small black aphids — most famously the black bean aphid — that cluster on the shoots, leaves, and pods of beans, dahlias, and other garden plants, sucking sap and stunting growth; gardeners battle it with soapy water, ladybirds, or insecticidal sprays. In North America, blackfly (often written as two words, black fly) refers instead to small hatching flies of the family Simuliidae — buffalo gnats — whose females bite people and livestock, sometimes in dense, maddening swarms near fast-flowing streams. The word is transparently formed from 'black' plus 'fly', and its plural is commonly unchanged. Its dual meaning makes context essential: a British allotment holder and a Canadian canoeist may use the same word for entirely different pests.
A small black aphid, especially the black bean aphid, which infests garden plants and crops.
"She pinched out the tips of the broad beans to keep the blackfly away."
This sense is dominant in British English, where blackfly is the standard counterpart to greenfly.
A small black bloodsucking fly of the family Simuliidae; a black fly.
"The blackfly were relentless along the riverbank at dusk."
This sense is the usual one in North American English, where the word is often written 'black fly'.
Gardeners typically treat blackfly as a mass noun with an unchanged plural; 'blackflies' appears more often when referring to individual biting flies.
"The crop was ruined by blackfly."
One gardener's blackfly is another continent's biting nightmare: in Britain it sucks sap from your beans, but in Canada it draws blood.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of blackfly
Blackfly is a straightforward compound of 'black', from Old English blæc, and 'fly', from Old English flēoge, meaning a flying insect. The compound arose naturally in English as a descriptive name for dark-coloured winged pests, with the aphid sense established in British horticultural language by at least the nineteenth century. It shares its elements with many other descriptive compounds such as blackbird and firefly, rather than descending from a classical root.
How blackfly is actually used
The word is most strongly associated with British gardening vocabulary, where it is treated as the dark counterpart to greenfly. In North American English, 'black fly' is more often written as two words and refers to the biting insect rather than an aphid. The plural is usually unchanged ('blackfly'), though 'blackflies' is also used, particularly in reference to the biting insect.
Easily confused with blackfly
Greenfly are aphids that are typically green in colour, whereas blackfly are the dark-coloured aphids of the same group.
In British gardening usage 'blackfly' means a plant-sucking aphid, while in North America it usually means the biting black fly (family Simuliidae) that swarms near rivers and bites people and animals.