DISTRIBUTION 367 



anura and Collembola, the last two feeding usually upon 

 minute particles of organic matter in the soil and being remark- 

 ably tolerant of extremes of temperature. The four chief 

 families of butterflies occur the world over, as do several fam- 

 ilies of beetles. Of species that are essentially cosmopolitan 

 we may mention the collembolan Isotoma fimetaria, and the 

 butterflies Vanessa cardui and Anosia plexippus, while among 

 beetles no less than one hundred species are cosmopolitan or 

 subcosmopolitan, including Tenebrio molitor, Silvanus suri- 

 namensis, Dermestes lardarius, Attagenus piceus and Calandra 

 oryzce. The coccinellid genus Scymnus occurs in North 

 America, Europe, Hawaii, Galapagos Islands and New Zea- 

 land, 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 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, according to 

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

 found; 20 occurring in South America, including the Gala- 

 pagos 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 

 instances of insects being taken alive far at sea ; Trimen men- 

 tions moths and longfcorn 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- 



