Insects at Rebecca Shoal and Tortugas. 197 



A second way by which insects may reach Rebecca Shoal light- 

 station is through the agency of birds. Several species, including the 

 man-o'-war bird, Fregata aquila; noddy, Anous stolidus; sooty tern, 

 Sterna fuscata; and the royal tern, Sterna maxima, occasionally light 

 upon the structure. It must be said, however, that no avian parasites 

 were found at the station. 



More important is a third method, the voluntary migration of 

 insects from the mainland or from islands. It is conceivable that 

 during calm weather such strong fliers as the Odonata, with certain Lepi- 

 doptera and Diptera, should voluntarily leave the Marquesas or Tor- 

 tugas Keys and fly in a direction which would bring them within sight 

 or smell of Rebecca Station. 



Finally, there is the wind as an agent for the distribution of insects. 

 It is well known that strong winds blow many Lepidoptera, Hymenop- 

 tera, Hemiptera,and Diptera out over large bodies of water, such as the 

 Great Lakes and seas. That large numbers of these fall into the water 

 and drown is evidenced by the masses of them washed upon the shores 

 by the waves; but it is not known what proportion of the insects sur- 

 vive to reach other shores. 



A priori, one would expect that the strong-flying species, such as 

 the bees and wasps among the Hymenoptera, Sphingidae of the Lepi- 

 doptera, and Tabanida; among the Diptera, if driven by a high wind 

 beyond sensing distance of land, would be more capable of sustaining 

 themselves in the air and so of being carried to safety than the heavy- 

 bodied, weak-flying insects like the Orthoptera and the flitting Lepi- 

 doptera. The habits of the latter accustom them to short flights and 

 considerable periods of rest. Of mosquitoes, it must be remembered 

 that, although they are comparatively small and not as a rule called 

 on to fly long distances in search of food, still they are light in weight, 

 have a relatively large wing surface, and are capable of sustaining 

 themselves in the air for long periods. The same is true of other small 

 Diptera, particularly the gnats. 



Several long migrations of mosquitos have been recorded. In his 

 book, "Mosquitoes," Dr. L. 0. Howard cites two remarkable flights 

 which were described in a letter to him from J. D. Mitchell, of Victoria, 

 Texas. In October 1879, during a strong east wind which had been 

 blowing for about 3 days, an immense swarm of mosquitoes migrated 

 in a line 3 miles wide and 50 feet high from a marsh 35 miles to the 

 eastward; 5 days were required for the passage. In 1886 a second 

 swarm traveled 50 miles along the west shore of Matagorda Bay in such 

 numbers that "they clouded the sky, bent down the grass with their 

 weight, and made all driftwood and ground the same color." 



Among the most important facts established by Dr. J. B. Smith 

 and his assistants during their investigations of the mosquitoes of New 

 Jersey in 1902-1904 were the length and frequency of the migrations 



