Insects at Rebecca Shoal and Tortugas. 205 



During the night of July 11-12 the wind veered again toward the 

 east; at 5 a. m. July 12 it was blowing freshly from east-southeast; 

 7 mosquitoes appeared between 9 a. m. and 2 h 20 m p. m. 



Judging from the direction of the wind previous to and during this 

 migration of July 11 and 12, we conclude that these mosquitoes were 

 carried from the shores of Cuba. The time required for the passage 

 was apparently less than in the earlier migration from Florida ; at the 

 end of only 10 hours after the wind, as noted at Rebecca Shoal, began 

 to blow from the southeast 8 p. m. to 5 h 30 m the following morning 

 the first mosquito appeared, whereas in the first case 27 hours were 

 required. Since the strength of the wind was similar in the two cases 

 this disparity in the time intervals may indicate that, while the second 

 flight may have left the Cuban coast at the point nearest to Rebecca 

 Shoal 95 miles directly south the first swarm probably took its 

 departure far up the west coast of Florida; for the nearest point, Cape 

 Sable, is only 105 miles from Rebecca. 



The fact that the great majority of mosquitoes taken belong to 

 the single species Aedes niger is evidence of its wide distribution and 

 common occurrence in the south. Furthermore, this distribution is 

 doubtless the result of the ability of these insects to sustain them- 

 selves in the air and so to be carried long distances across the sea by 

 winds. Howard, Dyar, and Knab give the range of this species as the 

 Antilles and Florida from Tampa southward. 



On July 13 the wind, east by south early in the morning, finally 

 settled into a strong and steady blow from due east and continued so 

 through the next 6 days. A single mosquito taken on the morning of 

 July 13 was the last which appeared during my stay at the lighthouse. 



As Smith has shown, mosquitoes do not rise from the ground while 

 strong winds are blowing. Had any been carried to the station it is 

 improbable that they could have made a landing even on the lee side 

 in the gale. 



Very important, as supplementing my experiences at Rebecca Shoal, 

 are observations made at Loggerhead Key by Dr. A. G. Mayer and 

 other investigators. On July 11 they noted, under similar wind con- 

 ditions to those at Rebecca Shoal, an unusual abundance of mosquitoes 

 and preserved 22 specimens, which proved to be of the same species, 

 A. niger. Dr. Mayer made the following record: 



"On the night of July 10, at about 8 p. m., there was a sudden squall with 

 rain from the southeast. By the morning of July 11 the wind was south to 

 south-southwest, blowing in a gentle south-southwest breeze all day. Mos- 

 quitoes were noticed at about noon of July 11, and became a pest by night, 

 so that we were unable to lie on the sand, as is our custom, at the southern 

 end of the island. Many of them were also found in the laboratory, and 

 they were thick in the bushes near the buildings and over the ocean about 

 300 feet from shore on the west side of the island. During the night of July 

 11 and 12 the wind veered to southeast to east-southeast, and the mosquitoes 

 practically disappeared." 



