DISTRIBUTION" 301 



molitor, Sili'iinns snn'iiamensis, Dermeslcs lurdarius. Attagenus piceus and 

 Calandra oryzcE. The coccinellid genus Scymnus occurs in North Amer- 

 ica, Europe, Hawaii, Galapagos Islands and New Zealand, and Anobium 

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

 odora, 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 Can- 

 ada. 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, according 

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

 20 occurring in South America, including the Galapagos Islands, n 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 in- 

 stances of insects being taken alive far at sea; Trimen 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 in- 

 stances 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 direc- 

 tion in which the Hessian fly spreads is determined largely by the pre- 

 vailing 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 pre- 

 vailing 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 distributed 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, 



Fresh-water streams convey incalculable numbers of insects in all 

 stages; and insects as a whole are very tenacious of life, being able to 



