1906] 
KXAB— SWARM IXG OF CULEX PIPIEXS 
125 
THE SWARMING OF CULEX PIPIEXS. 
BY FREDERICK KN'.\B, W.\.SHINGTON', 1). C. 
It ha.s been the writer’s good fortune to observe the swarming and mating of 
Culex u])on four consecutive evenings, ( Ictober 1.1-18, 1904. Many notices 
of the swarming of Culicidae and related forms have a])])eared, but most of the 
accounts deal with the swarming sini])ly as a remarkable phenomenon while its sig- 
nificance escaped them. It therefore seems worth while to record my own observa- 
tions. Following these I shall give the more interesting data of j)revious writers, 
and at the end, a bibliography of the subject. 
iMy observations were made at Urbana, Illinois, under exceptionally favorable 
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, (hiring dry weather, liecomes jiractically stagnant. About 
a mile up the stream the water was polluted by the discharge from an abattoir. The 
foulne.ss 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. Fiarly in 
October the writer found the larvae of Culex pipiens present in immense numbers, 
and when the shrubbery bordering the stream was disturbed the imagos rose in 
great clouds. '^Idiese mosipiitoes, however, showed no inclination to leave the water- 
side and would quickly return to the shelter of the marginal vegetation. 
October 1.1 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 a])])ears to be perfectly still. 
-\t 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 intervening 
line of tall trees. IVhen near the middle of the field a cloud of mosquitoes was 
noticed directly overhead. The lowest mosejuitoes 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-keyi'd pijiing, vibrating between two 
notes in con.stant rajiid reiteration, was very distinct. ’Fhe variations in tone seemed 
to correspond to the upward and downward movements of the individuals, lu the 
light of the succeeding observations it would seem that this swarm had been formiug 
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 
