THE YELLOW-FEVER MOSQUITO. 7 
54° to 57° F. it becomes torpid, flies with difficulty, and no longer 
stands firmly on its legs. It dies quickly when the temperature is 
at the freezing point. When exposed for a brief period to a tem- 
perature of 49° and then placed in a warm room it will revive, but 
it dies at a temperature of 39° maintained for more than an hour. 
It may be kept alive for some time at temperatures of 45° to 48°. 
DISTANCE OF FLIGHT. 
~ The yellow-fever mosquito is a strong flier; nevertheless, it does 
not fly very far and, as has been already pointed out, is rarely found 
away from houses. It apparently never flies very high and is found 
by preference in the lower stories of houses. There is conflicting evi- 
dence regarding the effect of a strong current of wind on this species, 
and it is recorded that strong air currents produced by a mechanical 
ventilator had no effect upon flight. Other observers have searched 
for it in vain in situations exposed to the wind. 
The distance of flight has an important bearing upon the distance 
at which ships should be anchored from fever-infected ports, but 
with vessels anchored at given distances it is most difficult to deter- 
mine whether yellow-fever mosquitoes which may be found on 
board have flown from the shore or have been carried by boat parties 
visiting the vessel, perhaps concealed under coat collars or hidden 
in other parts of clothing. There is no positive evidence that vessels 
anchored more than half a mile from the shore will be visited by the 
‘yellow-fever mosquito by natural flight. : 
DISTRIBUTION BY ARTIFICIAL MEANS. 
Although, as indicated in the preceding section, the yellow-fever 
mosquito apparently does not fly far, it is readily carried to great 
distances accidentally by artificial means. Vessels, once infested, 
may carry the species to far-distant ports. The yellow-fever mosquito 
has been found in New York upon vessels coming from Vera Cruz, 
and it is by such carriage of infected mosquitoes that the early out- 
breaks of yellow fever in Philadelphia and other northern cities are 
to be accounted for. 
Railway trains also carry this mosquito, frequently in large num- 
bers. It has spread inland from Vera Cruz, first to Cordoba and later 
to Orizaba, entirely by means of the railway. Almost every summer 
the yellow-fever mosquito is carried in railroad cars from New 
Orleans, Mobile, and other southern cities, on through trains, to 
Washington, Baltimore, and New York. It has been seen and cap- 
tured on these trains by competent entomologists. 
BAT 
