From arab; a mosquito (from its swarming) -- divers sorts of flies, swarm.
see HEBREW arab
H6157. arob
עָרֹב9 noun masculineExodus 8:20 probably swarm (mixture, from incessant, involved motion; LagBN 112 doubts); — of plague of stinging flies, coming in a swarm (see DiEx) 8:17 (twice in verse) + 5 t. 8(J), Psalm 78:45; 105:31.