108 (}eu(jraphicul Distribution of Insects. 



cies possess greater poAvers of flight, and that it will conse- 

 tpently operate chiefly on the diurnal Lepidoptera, the Hy- 

 menoptera, the Diptera, and a few Orthoptera, which are 

 most remarkable in this respect. One of the most interesting 

 examples that can be cited of the diff"usion of a species from 

 this cause, is that of the bees brought from Europe to North 

 America. They have again become, as is well known, ahuost 

 completely wild. According to M. Warden,* the common 

 hive-bee was unknown, in 1797, to the west of the Mississippi. 

 Fourteen years after, it had not only crossed that river, but 

 had ascended its course, as well as that of the Missouri, to a 

 distance of six hundred miles. It had thus advanced at the 

 rate of forty-three miles yearly. 



Causes of Stations and Habitats. — AVe now come to inquu'e 

 Avhether stations and habitations can be explained by all the 

 physical conditions which have been alluded to. With regard 

 to stations, the case seems not at all doubtful. An insect in 

 this resembles all other animals, that it can live in a locality 

 only as long as it finds there the conditions of nom-ishment, 

 temperature, light, &c. necessary to its existence, and as long 

 as other organized beings do not drive it away. It will mul- 

 tiply the more abundantly within the limits assigned to its 

 species, if these conditions are united in a high degree, and if 

 some of the principal of them are Avithdrawn, it wUl either 

 (juit the locality in question or perish. 



Still, when we come to the actual application, we often find 

 it very difticult to explain certain diversities of station observed 

 among species of the same genus, whose habits are entirely 

 alike. For example, M. Humboldt has noticed (and M. Lacor- 

 daire has made the same observation in Guiana) that in the deep 

 forests of the Orinoco, notwithstanding an entire similarity in 

 the conditions of temperature, humidity, light, &c. the different 

 v^Yecve^oi Maringouins (or musquitoes) are stationed in very re- 

 stricted localities, in so much that each canton and each river 

 possesses its pecuUar species which never leave it nor mingle 

 with the neighbouring species. In such cases, there must be 



• Essai statistiqiie, politique, ct historique, sui- les Etats-unis d'Amerique, 

 to'ii. iii. p. 139. 



