346 MOSQUITOES OF NORTH AMERICA 



would start an epidemic which would progress gradually inland from the water 

 front, as was the case in Philadelphia and in other places. The same method of 

 travel accounts also for the European outbreaks. The shortening of sea voyages 

 by the introduction of steam has, in a way, increased the possibility of mosquito 

 carriage from one place to another; but, in another way, it has lessened this 

 possibility, since the water supplies of ships are of late years, as a rule, so kept 

 that mosquitoes can not breed in them. 



The natural geographical distribution of the yellow-fever mosquito, now well 

 known to coincide with the tropical and subtropical life zones, does not limit its 

 possibilities in this direction. As is shown in the section on the geographic dis- 

 tribution in the United States the yellow-fever mosquito is often found in mid- 

 summer or late summer breeding north of its permanent range, only to die out 

 there with the winter. This can be only when it is carried north by artificial con- 

 veyances during the summer, flying out and breeding for a generation or so 

 where proper breeding-places are at hand. Thus, in August, 1904, it was found 

 to be breeding on the grounds of the Exposition at St. Louis. The yellow-fever 

 mosquito is particularly adapted to such carriage. In the late summer of 1908 

 one was found in Washington, D. C, in all probability brought up from the 

 South on a through train over one of the southern railroads. 



One of the writers (Howard) has often gone to bed in a sleeping car at New 

 Orleans and suffered all night from mosquitoes which were carried along with 

 the train. Mr. J. 0. Martin, an entomologist and good observer, in September, 

 1901, coming to Washington on the train from New Orleans, noticed that at 

 nightfall the train stopped in a swamp just outside of New Orleans, and mos- 

 quitoes came in through the open windows in very large numbers. Mr. Martin, 

 knowing what had been written about the carriage of mosquitoes by railroad 

 trains, noticed carefully the rest of the journey and states that a considerable 

 proportion of the mosquitoes which entered the train just outside of New 

 Orleans were still in the train on its arrival in Washington. 



A number of instances have been published where mosquitoes were introduced 

 into new localities by the rearrangement of trains and the putting on of night 

 trains on railroads where there had previously been no night service. Some of 

 these are mentioned in " Mosquitoes " (Howard) . One of these instances relates 

 to the introduction of mosquitoes into the City of Mexico. Since its publication 

 the writers have been informed by Prof. A. L. Herrera, of the City of Mexico, 

 that the statement that mosquitoes were first brought to the City of Mexico from 

 Vera Cruz on the completion of the railroad from the gulf to the city, is in- 

 correct, but that they first made their appearance in the City of Mexico in 1885, 

 on the completion of the Mexican National Eailroad, having been brought down 

 from the valley of the Eio Grande at Neuvo Laredo. Prof. Herrera further 

 stated that during the summer time almost every train from the north brings 

 many mosquitoes down to the City of Mexico. These escape from the cars, take 

 advantage of the abundant breeding-places and soon multiply excessively. This 

 statement was made in 1902. Since that date the admirable sanitary work in 

 the City of Mexico, under the direction of Dr. Liceaga, has greatly reduced the 

 mosquito breeding-places of that city. 



