Swarms, consisting apparently of males only, respond to simple sounds produced by an audio-oscillator through loud speakers. A startle response occurs when sounds between 80 and 800 cps are broadcast to the swarms at intensities above about 80 db. A second response, an agitated circling and gathering around the sound source, occurs only near 125 and 250 cps, at intensities of 13–18 db. above ambient noise levels for 125 cps, and 3–8 db. for 250 cps. The second reaction, because of its sharply tuned frequency determination and occurrence at remarkably low intensities, could have significance in mating or swarming. The frequency of the male wing sound is about 600 cps, and broadcasts of recorded samples of this to the swarms had no effect. No females were captured at any time; thus the frequency of the female wing sound is unknown. The possible biological significance of the reaction was not determined.