SWARMING OF ANOPHELES 127 



regarding the mating habits in the genus Anopheles, the following notes are 

 oft'ered. Much to his surprise the writer found that the males of Anopheles 

 swarm as do those of Ciihx, although the behavior in the two forms is quite dif- 

 ferent. 



" The observations were made on Plumraers Island (Maryland) in the 

 Potomac River, about ten miles above Washington. Near the highest part of 

 the island is a ledge of rock forming an open space surrounded by the woods on 

 three sides. The side towards the river is open, save for a couple of small trees 

 at the edge, and terminates in a nearly perpendicular cliff. On October 7, 

 shortly before 5 o'clock, the writer visited the spot to enjoy the sun-set. The 

 ledge is about sixty feet above the water and on its highest part, where some tufts 

 of tall grass grow in a crevice of the rock, was a swarm of dancing Diptera. The 

 swarm was directly over the tufts of grass, its base seven or eight feet from the 

 ground, the apex five or six feet higher. Although in appearance and action 

 quite unlike Culex pipiens (observed on previous occasions) they were recognized 

 as mosquitoes by the prominent palpi and the plumed antennae. With a sweep 

 of the net fifteen were secured and proved to be males of Anopheles punctipennis. 

 Their appearance in flight difl'ered from pipiens mainly by the position of the 

 legs which were held straight behind and close together. The palpi and antennae, 

 directed straight forward, also appeared much more prominent than in pipiens, 

 which, together with the much longer legs, extending out behind, gave them a 

 very characteristic appearance. 



" In their actions, too, they differed markedly from pipiens. The swarm was 

 small, composed of less than a hundred individuals, and was not as compact as 

 the swarms of pipiens. The movements of these males were far more free and 

 varied than those of pipiens which constantly repeat the same circumscribed 

 movements. The Anopheles flew about in the swarm in a circling upward or 

 downward ' corkscrew ' course. Their movements were more rapid than those of 

 pipiens and often irregular; single individuals would at times leave the swarm, 

 and cutting a wide circle, return into it. Sometimes these stray individuals 

 would fly for a short distance with a peculiar rapid zig zag motion — a series of 

 short sidewise jerks — and then return with the ordinary steady flight. In spite 

 of these varied evolutions the mosquitoes showed a tendency to face in one 

 direction, presumably towards the wind, although the evening M^as perfectly calm 

 and there was no breeze apparent. As it began to darken the males began to 

 leave the swarm one by one, flying upward, either into surrounding trees or more 

 often they would disappear into the sky. On this evening copulation was not 

 observed and from the following observations it may be assumed that union only 

 takes place during the early part of the swarming. 



" Although stormy and cold weather intervened, the following Sunday proved 

 fine and the ledge on the island was again visited. Shortly before 5 o'clock, 

 with the sun still shining but near the horizon, a few males were found already 

 assembled and engaged in their circling flight above the grass-tufts. Others 

 came from different directions and joined the swarm and by sunset it consisted 

 of perhaps sixty or seventy mosquitoes. It was difficult to follow the movements 

 of single mosquitoes but it seemed that in circling about they described a figure- 

 of-eight — sometimes on a plane, or ascending and descending. At 5.15 a pair 

 was seen falling out of the middle of the swarm, grappling each other as they 

 fell. They had not dropped far below the swarm when union was effected, and, 

 swinging out in opposite directions, still united they drifted slowly away towards 

 the ground. Within ten minutes six pairs were seen to drop out of the swarm 

 and copulate in this manner but after that no more. Three of the pairs were 

 captured in the net ; one pair rested in the bottom of the net about a minute, 

 then separated and flew out; the other two pairs remained united even after 



