Origin: before 900; (noun) Middle English; Old English swearm; cognate with German Schwarm swarm, Old Norse svarmr tumult; (v.) Middle English swarmen, derivative of the noun
"to climb by clasping with the arms and legs alternately," 1550, perhaps originally a sailors' word, of uncertain origin. Also recorded as swarve (16c.) and in Northern dialects swarble, swarmle.