360 DARWINISM chap. 



in Lat. 6° N., Long. 22 J° W., being between the former position 

 and Sierra Leone, thus rendering it probable that the moths 

 came from that j^art of the African coast, in Avhich case the 

 swarm encountered by the Pleione must have travelled more 

 than 1200 miles. 



A similar case Avas recorded by ]\Ir. F. A. Lucas in the 

 American periodical Science of 8th April 1887. He states 

 that in 1870 he met with numerous moths of many species 

 while at sea in the South Atlantic (Lat. 25° S., Long. 24° W.), 

 about 1000 miles from the coast of Brazil. As this position 

 is just beyond the south-east trades, the insects may have been 

 brought from the land by a westerly gale. In the Zoologist 

 (1864, p. 8920) is the record of a small longicorn beetle which 

 flew on board a ship 500 miles off the west coast of Africa. 

 Numerous other cases are recorded of insects at less distances 

 from land, and, taken in connection Avith those already given, 

 they are sufficient to show that great numbers must be con- 

 tinually carried out to sea, and that occasionally they are able 

 to reach enormous distances. But the reproductive powers of 

 insects are so great that all we require, in order to stock a 

 remote island, is that some few specimens shall reach it even 

 • once in a century, or once in a thousand years. 



Insects at great Altitudes. 



Equally important is the proof we possess that insects are 

 often carried to great altitudes by upward currents of air. 

 Humboldt noticed them up to heights of 15,000 and 18,000 

 feet in South America, and ^Ir. Albert Miiller has collected many 

 interesting cases of the same character in Europe.^ A moth 

 (Plusia gamma) has been found on the summit of Mont Blanc ; 

 small hymenoptera and moths have been seen on the Pyrenees 

 at a height of 11,000 feet, while numerous flies and beetles, 

 some of considerable size, have been caught on the glaciers 

 and snow-fields of various parts of the Alps. Upward 

 currents of air, whirlwinds and tornadoes, occur in all parts 

 of the world, and large numbers of insects are thus carried 

 up into the higher regions of the atmosphere, Avhere they 

 are liable to be caught by strong winds, and thus conveyed 

 enormous distances over seas or continents. With such 

 1 Tnuis. Ent. Soc, 1871, p. 184. 



