130 MOSQUITOES OF NORTH AMERICA 



where they, especially towards evening, flock together in dancing swarms and 

 tempt the females to come up by the noise of their wing-beats. 



" When a female comes up into this dancing cloud it is chosen by a male and 

 the two separate them8elves from the rest, while the male swarm continues the 

 dancing with uninterrupted music at varying heights in the air." 



The swarming of Aedes spencerii has also been observed by Ivnab, on the Sas- 

 katchewan prairies. This is described in Smithsonian Miscellaneous Collec- 

 tions, volume 50, part 4, pages 542-544. 



" Adults of this species first appeared active on May 30 and a few came to 

 bite. They were first noted in numbers on June 5, a warm, sunny day follow- 

 ing four days of cold, cloudy weather. They came drifting before the wind, and 

 during calm intervals were very annoying. At 10.45 a. m., on a rise of ground 

 west of the town, the highest rise on that part of the prairie, a swarm of about 

 50 males gathered above my head. They emitted a high-keyed piping sound, 

 swinging backward and forward and swaying sidewisc, all the time facing the 

 wind. With every gust of wind they were scattered toward the ground, only to 

 reassemble when the wind decreased. When I passed the place again, at 12.45 

 p. m., the males were still in evidence, although much interfered with by the 

 wind. The same day, at 5.30 p. m., another swarm of males was observed in the 

 upper part of a ravine, where the slopes were gentle. They were going through 

 rapid evolutions, darting forward and upward and dropping back again, but 

 without unison. When disturbed by the wind their flight became more rapid, 

 and sudden gusts caused them to fly to the ground. Several pairs were seen 

 flying off in copula, and once the female was observed approaching the swarm 

 from beneath. There was a second swarm of males farther down the ravine, 

 about half way up the slope, and, like the other, at the margin of the shrubbery 

 filling the bottom of the ravine. In this case a swann of very small Chironomids 

 was mixed with the lower part of the swarm. In crossing an open field in the 

 river valley at 6.30 p. m. a swarm of males formed over my head and, following 

 me, increased to the number of perhaps two hundred. They disappeared when 

 I approached the woods on the edge of a ravine. This experience was repeated in 

 the field beyond, and upon nearing the edge of the woods the swarm again de- 

 parted and could be seen in the middle of the field. Several days of cold and 

 cloudy weather followed, during which the mosquitoes remained quiescent. 

 After the heavy rain of the previous night, the afternoon of June 9 was warm 

 and sunny and the mosquitoes exceedingly abundant and active. At 6.30 p. m. 

 I walked toward the river with a companion. As soon as we had left the town 

 the female mosquitoes began to rise out of the grass and alight upon us. There 

 was a brisk breeze blowing and the mosquitoes settled on the leeward side of our 

 bodies, and a cloud of them followed us, keeping for the most part about our legs. 

 These clouds increased rapidly and became very aggressive as we passed down 

 into the valley, where we came upon a cloud of males on the open prairie. When 

 Ave approached them they formed in two swarms over our heads. My companion, 

 being the bulkier man, attracted a much larger swarm. We thus each had two 

 swarms of mosquitoes about us ; the one, of females, kept about the lower part of 

 our bodies, while the other one, of males, kept above our heads. Several copula- 

 tions were noted. Upon entering a ravine the males all left us and only a part of 

 the females followed. Upon emerging on the other side of the ravine a new 

 swarm of females quickly gathered, and shortly we came upon another large 

 swarm of males, which again concentrated above our heads in separate swarms. 

 It was now 7 o'clock, but still bright daylight at this season of the year. The 

 swarms of males I judged to contain many hundreds, if not a thousand, indi- 

 viduals. These swarms, in close formation, followed us up the long hill and 



