MATING HABITS 121 



The attitude assumed during the copulatory act differs according to the struc- 

 ture of the claws of the female. In the forms with simple claws (Cnlex, Anoph- 

 eles) the position is end to end, the pair facing in opposite directions. The forms 

 in which the female claws are toothed copulate face to face, clasping each other 

 with their claws. The first exact observation of the mating habits of mos- 

 quitoes was based on such a species (Aedes calopiis) and to this may be traced 

 the repeated statement that mosquitoes all copulate in this way. This early 

 account, by Godeheu de Eiville, will be found abstracted in the chapter on the 

 yellow-fever mosquito (p. 276). 



One of us (Knab) has published his observations on the mating-habits of mos- 

 quitoes in a series of papers which are brought together here. The first is on 

 the swarming of Culex pipiens (Psyche, October, 1906, pp. 133-133), and is 

 based on observations made by himself in Illinois, and in it he includes accounts 

 of many former observations. The general question of swarming and mating 

 as considered in this article is herewith largely quoted from : 



" It has been the writer's good fortune to observe the swarming and mating of 

 Culex pipiens upon four consecutive evenings, October 15-18, 1904. Many 

 notices of the swarming of Culicidse and related forms have appeared, but most 

 of the accounts deal with the swarming simply as a remarkable phenomenon 

 while its significance escaped them. It therefore seems worth while to record 

 my own observations. Following these I shall give the more interesting data of 

 previous writers, and at the end, a bibliography of the subject. 



" My observations were made at Urbana, Illinois, under exceptionally favor- 

 able conditions. Although the country about TJrbana is well drained and there 

 is but little water, mosquitoes were remarkably abundant. As far as could be 

 determined all came from one source. On the outskirts of the town is a small 

 stream, known as the Salt Fork, which, during dry weather, becomes practically 

 stagnant. About a mile up the stream the water was polluted by the discharge 

 from an abattoir. The foulness of the water was such that the fish normally 

 present in the stream were all destroyed and thus an ideal breeding-place for 

 mosquitoes was created. Early in October the writer found the larvae of Culex 

 pipiens present in immense numbers, and when the shrubbery bordering the 

 stream was disturbed the images rose in great clouds. These mosquitoes, how- 

 ever, showed no inclination to leave the water-side and would quickly return to 

 the shelter of the marginal vegetation, 



" October 15 was a warm autumn day and its close was marked by one of 

 those clear calm evenings when not a leaf stirs and the air appears to be perfectly 

 still. At five o'clock the writer was crossing a corn-field not far from the stream. 

 The sun was already near the horizon and its direct rays were cut off by an in- 

 tervening line of tall trees. When near the middle of the field a cloud of mos- 

 quitoes was noticed directly overhead. The lowest mosquitoes were about the 

 writer's head and shoulders, the topmost ones perhaps five feet higher; the 

 transverse diameter of the swarm was about two feet. The high-keyed piping, 

 vibrating between two notes in constant rapid reiteration, was very distinct. 

 The variations in tone seemed to correspond to the upward and downward move- 

 ments of the individuals. In the light of the succeeding observations it would 

 seem that this swarm had been forming above the writer's head from the time he 

 entered the field. The swarm was watched for about twenty minutes. The 

 individuals in the swarm flew up and down amongst each other with a kind of 

 weaving motion — a downward and forward plunge and back again, performed 

 without unison or regularity. The movements were sufficiently slow to allow 



