342 MOSQUITOES OF NORTH AMERICA 



bay cedar bushes, cactus, and coarse grasses, and it is certain that there are no 

 natural breeding places for mosquitoes within the group. 



" On Garden Key Stegomyia {^Aedes calopus] breeds within the numerous 

 cisterns of Fort Jefferson, No mosquito larvse have ever been seen during ten 

 years of observation in the cisterns of the light-house on Loggerhead Key ; this 

 being doubtless due to the purity of the water which is collected upon slate roofs 

 and runs at once into the concrete cisterns. 



" The iron cisterns of the Carnegie Institution Laboratory, also on Logger- 

 head Key, are covered with kerosene oil, and no mosquitoes breed within them. 

 All tin cans and garbage on Loggerhead Key are towed daily out to sea and cast 

 over-board. 



" I mention these details merely to show that mosquitoes can breed only on 

 Garden Key, Tortugas, the other Islands of the group affording no suitable places 

 for this purpose." 



Dr. Mayer informs us that no mosquitoes other than Aedes cdlopus breed 

 upon the Tortugas and that the nearest breeding-grounds for other species are 

 upon the Marquesas Keys which are the lands nearest to the Tortugas group, and 

 lie 40 nautical miles to the eastward of Loggerhead Key. The Marquesas are 

 low-lying mud flats covered by a dense growth of mangrove bushes and Dr. 

 Mayer states that myriads of mosquitoes breed there during the summer season. 

 " On damp, but rainless days, when the sky is over-cast, and the wind blows from 

 Marquesas toward the Tortugas, mosquitoes in considerable numbers suddenly 

 appear upon Loggerhead Key. They also drift upon the Tortugas during damp 

 moonlight nights, but it is remarkable that when the wind shifts and blows from 

 some direction other than that from the Marquesas the mosquitoes disappear 

 from Tortugas in a few hours." At our request. Dr. Mayer has secured a speci- 

 men of one of these mosquitoes which he secured in 1910. It proved to be 

 Aedes niger, the Antillean form of Aedes tceniorhynchus which extends over to 

 Florida. The last-named species is the one for which the migratory habit is 

 best established. Dr. Mayer even thought that mosquitoes occasionally crossed 

 from Cuba, a distance of 90 miles, but such a distance is considerably in excess 

 of anything observed by others. It must be considered that Dr. Mayer's state- 

 ments, as well as those of others, are based upon the assumption that the mos- 

 quitoes are carried by the wind or fly with it. This is by no means demonstrated. 



Other observers have found that these mosquitoes fly against the wind. One 

 of us (Knab) has observed that in Saskatchewan the most abundant mosquito 

 of that region {Aedes spenceri) flies against a strong wind. Mr. A. H. Jennings 

 has informed us that in his investigations in Panama he found that Anopheles 

 invariably flew against the wind. With reference to Prof. Mayer's belief that 

 mosquitoes fly from Cuba to the Tortugas, a distance of 90 miles, we could 

 only accept this in the presence of convincing proof. Investigations will have to 

 be carried on much more thorouglily before any conclusion can be reached re- 

 garding the origin of the mosquitoes found in the Dry Tortugas. 



In August, 1909, many newspapers contained accounts of the appearance of 

 a swarm of mosquitoes in the Gulf of Mexico, sixty miles from the nearest land, 

 and on August 24 a sheet of marine data from the U. S. Hydrographic Office was 

 received at the Bureau of Entomology, filled out by Captain Young of the steam- 



