DISTRIBUTION 207 
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 /sotoma fimetaria, and the 
butterflies Vanessa cardui and Anosia plevippus, 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 
oryse. The coccinellid genus Scymnius 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, 11 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 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- 
