A locust was an insect from Earth, known for its destructive impact on agriculture.
In 2369, Rumpelstiltskin told Miles O'Brien a story about a farmer from Derry who had tried to chase him away before he saved the farmer's crop from locusts. (DS9: "If Wishes Were Horses")
In a vision experienced by Benjamin Sisko in 2373, he saw a swarm of billions of locusts appear in the sky above Bajor before traveling to Cardassia Prime. (DS9: "Rapture") These "locusts" later turned out to be the Dominion fleet that arrived after the Cardassian Union joined. (DS9: "In Purgatory's Shadow", "By Inferno's Light")