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 (Culex, 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 (Aédes calopus) and to this may be traced 
the repeated statement that mosquitoes all copulate in this way. This early 
account, by Godeheu de Riville, 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. 123-133), 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: 
“Tt 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 Culicide 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 Urbana 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 larvee of Culex 
pipiens present in immense numbers, and when the shrubbery bordering the 
stream was disturbed the imagos 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 
