

DISTRIBUTION 323 



dred species are cosmopolitan or subcosmopolitan, including Tenebrio 

 molitor, Silvanus surinamensis , Dermestes lardarius, Attagenus piceus 

 and Calandra oryzce. The coccinellid genus Scymnus occurs in North 

 America, Europe, Hawaii, Galapagos Islands and New Zealand, and 

 Anobium and Hydrobius are distributed as widely. The huge noctuid, 

 Erebus odor a, occurring in Brazil on the lowlands, and in Ecuador at an 

 altitude of 10,000 ft., finds its way up into the United States and even 

 into Canada. The chinch bug and many other Central American forms 

 also spread far northward, as described beyond. 



Means of Dispersal. This exceptional range of insects is due to 

 their exceptional natural advantages for dispersal, chief among which 

 are the power of flight and the ability to be carried by the wind. The 

 migratory locust, Schistocerca peregrina, has been found on the wing five 

 hundred miles east of South America. The home of the genus, accord- 

 ing to Scudder, is Mexico and Central America, where 23 species are 

 found ; 20 occurring in South America, including the Galapagos Islands, 

 1 1 in the United States and 6 in the West Indies ; and there is every 

 reason to believe that S. peregrina the biblical locust and the only 

 representative of its genus in Africa crossed over from South America, 

 where it is found indeed at present. Darwin and others have recorded 

 many instances of insects being taken alive far at sea; Trim en mentions 

 moths and longicorn beetles as occurring 230 miles west of the African 

 coast and Sphinx convolvulus as flying aboard ship 420 miles out. In 

 these instances the insects have usually been assisted or carried by 

 strong winds, particularly the trade-winds, and oceanic islands have 

 undoubtedly been colonized in this way. On land, Webster has found 

 that the direction in which the Hessian fly spreads is determined largely 

 by the prevailing winds at the time when these delicate insects are on 

 the wing, and that the San Jose scale insect spreads far more rapidly 

 with the prevailing winds than against them, the wind carrying the 

 larvae as if they were so many particles of dust. The pernicious buffalo- 

 gnat of the South emerges from the waters of the bayous and may be 

 carried on a strong wind to appear suddenly in enormous numbers 

 twenty miles distant from its breeding place. Mosquitoes are dis- 

 tributed locally by light breezes, but cling to the herbage during strong 

 winds. 



Ocean currents may carry eggs, larvae or adults on vegetable drift 

 to new places thousands of miles away. Thus the Gulf Stream annually 

 transports thousands of tropical insects to the shores of Great Britain, 

 where they do not survive, however. 



