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Means by Which Insects May Reach the Station

mosquitoes, wind, species, rebecca and miles

MEANS BY WHICH INSECTS MAY REACH THE STATION.

There are four conceivable ways in which insects may reach Rebecca Shoal light-station. First by boat, for many are brought in provisions and other stores. Several species of larder pests, including two weevils and a flour beetle, two species of moths, one in flour and another in raisins, and an occasional fruit-fly, were observed on the station. The light-house power-boats usually bring on each trip a few house-flies and occasionally a blow-fly. In one instance a Tabanus was introduced.

It is extremely improbable that insects are attracted to the station from vessels which must pass through Rebecca Channel at a distance of at least 0.5 mile. Indeed none of the half dozen house-flies left the yacht Anton Dohrn on her voyage from Tortugas to Key West on July 30, although she passed within 100 yards of the Rebecca station. It is inconceivable that flies or mosquitoes voluntarily leave the solid support of a vessel where food is close at hand and its odors strong in order to land on a small light-station at a considerable distance. Any one who has been on board ship at sea has probably observed how closely flies, beetles, dragon-flies, and moths keep to the vessel.

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, Anotis stoliclue; 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, Sphingidie of the Lepi doptera, and Tabanidie 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. O. 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 undertaken by the three species, Aedes 8011iCiiatIS, A. cantator, and A. tceniorhynchus. Breeding only in the salt marshes along the seashore, swarms of these three species migrate inland for distances of more than 30 miles; although capable of making these flights in calm weather, favorable sea breezes were found to hasten them.

As stated above, Dr. Mayer and others have noted in previous years that mosquitoes were abundant on Loggerhead Key only after the wind had been blowing from a certain quarter, usually the north east or north, for a considerable period. Furthermore, a change of the wind into the east or west was always followed by a marked falling off in the numbers of mosquitoes encountered about the laboratory. The inference was that the northerly wind had blown large swarms of the insects away from the west coast of Florida and that part of them had reached Tortugas. If this inference were correct, even a small building, such as the Rebecca Shoal light-station, lying out in the ocean 18 miles east of Loggerhead, should form a sufficiently large support to attract a few mosquitoes which might be carried into its immediate vicinity. Even during a wind of such strength that the insects could not retain a foothold upon the windward side of the station, they would be able to do so under its lee.