344 MOSQUITOES OF NORTH AMERICA 



at Montevideo and at Ilha Grande shows that this distance does not afford such 

 protection and that the crew of a ship in any port, of the harbor of Eio for 

 example, is liable to be infested by mosquitoes." 



Of course Manson meant infested by Anopheles or other disease-bearing mos- 

 quitoes. Surgeon Eussell found Anopheles only in one case; and its presence 

 on board ship about two miles from shore can not be accepted as proof that 

 the mosquito had flown this distance. 



It is evident from the foregoing that the mosquitoes concerned in migrations, 

 in the strict sense of that term, are the coast species of Aedes. In the regions 

 we have under consideration in this work the species concerned are Aedes 

 tceniorhynchus, A. niger, A. sollicitans and, along the northern portion of the 

 Atlantic coast, Aedes cantator. It appears from the observations of H. J. Quayle 

 that on the California coast Aedes quaylei and Aedes squamiger behave in a 

 similar manner. 



Only the females are concerned in these migrations and there is little reason 

 to doubt that their object is to obtain food. It is probable that those females 

 which obtain blood and survive accidents return to the salt marshes to deposit 

 their eggs. It is doubtful, however, that in these migrations the wind is a neces- 

 sary factor or even that, in most cases, it has an important influence. In other 

 words we must consider those cases in which large swarms of mosquitoes are 

 said to have been carried a considerable distance by the wind as problematical. 



The following observations, in so far as they relate to one of the so-called 

 house mosquitoes, which have entirely different habits from those already con- 

 sidered, are of some interest. We quote directly from " Mosquitoes in Hawaii " 

 by D. L. Van Dine : 



" The writer has not observed evidences of migration among the species of 

 mosquitoes occurring in these Islands. Invariably the source of mosquitoes in- 

 festing any district has been found to be nearby natural and artificial collections 

 of water, usually artificial collections in the immediate vicinity, Mr. [H. W.] 

 Henshaw, in speaking of invasions of mosquitoes, says in a letter to the writer : 



" So far as my own observations extend such accidental invasions of mos- 

 quitoes are rare in these Islands, the insects here as a rule being extremely local. 

 Nevertheless that such accidental dispersal of the pests in the Islands does 

 actually occur is proved by an instance in point which came under my personal 

 observation in June, 1899, at Pahala, Kau (Island of Hawaii). Mr. C. M. 

 Walton, the then manager of the plantation, informed me that prior to the visi- 

 tation of the pests about to be described, mosquitoes were practically unknown 

 about the village ; if found at all it was in such small numbers as to cause no 

 annoyance, and mosquito-nets were unknown. 



" In the spring of 1899 there was an unusual quantity of waste water from the 

 mill and this ran down to the flats about a mile below and there formed a series 

 of small ponds aggregating a considerable expanse of shallow water. Not long 

 after the formation of the ponds swarms of mosquitoes made their appearance 

 about the mill and in all the dwellings, evidently brought there by the strong 

 trade winds which blew directly from the ponds. At the time of my visit the 

 mosquitoes (Culex pipiens *) put in an appearance about dusk and soon ren- 

 dered life a burden and sleep impossible except under nets which every house- 

 holder had been compelled to provide for every bed. 



♦ The mosquito under consideration is Culex quinquefasciatus. Say. 



