212 CHAPTER II 



p. 316) has already drawn attention to this remarkable fact, as far as Diplopods 

 are concerned. 



Thd situation is well-known also to applied entomologists. They noticed that 

 the number of originally European insect pests in North America is higher than that 

 of originally American ones in Europe. A few instances of the latter type are 

 mentioned below (p. 222), the most famous being the Colorado Beetle {Leptino- 

 tarsa decemlineata Say), the Grape Phylloxera {Phylloxera vitifoliae Fitch), and 

 the Woolly Aphis [Eriosoma lanigerum Hausm.). "The Fall Webworm" {Hyphan- 

 tria cunea Drury) has become a potential pest in southeastern Europe. "The 

 Northern Army Worm" {Leucania unipuncta Haw.), with an almost cosmopolitan 

 distribution, is also said to be of North American origin. 



Still more insignificant is the group of American animals not associated with 

 agricultural plants which have been unintentionally introduced into Europe and 

 become naturalized outdoors. For instance, only two cases of this kind have been 

 observed among the Coleoptera: the Longicorn beetle Neoclytus acuminatus F. 

 and the small Weevil Stenopelmus rufinasus Gyll. Both are now widely distributed, 

 the former in the regions surrounding the northern part of the Adriatic Sea, the 

 latter in western Europe. Both have been imported with their foodplants, the 

 Neoclytus (arrived before 1850; Miiller, 1949-53, p. 148-149) with American tim- 

 ber, the Stenopelmus (since 1898) with the water-fern Azolla caroliniana Willd. 

 which is of North American origin but generally cultivated in Europe as an orna- 

 ment in ponds and pools. 



This is fully in accordance with the geographical character of the European 

 flora. It has sent hundreds of emigrants west across the Atlantic, which is illustra- 

 ted above on the Newfoundland flora (p. 146) and the vegetation of the English 

 ballastplaces (p. 196; vide also Gilmore, 1932), but weeds and other recent in- 

 troductions originating in North America, completely naturalized and widely 

 distributed in Europe, are surprisingly scarce. Well-known instances are^: — 



Elodea canadensis Michx.^ — Transamerican, N to N. Labr. — Europe (widely, 

 since 1836), N to N Sweden. 



Epilobium glandtdosum Lehm. (incl. adenocaulon Haussk.)^ — Transamerican. — 

 Europe (widely, since later part of 19th century), N to C Finland. 



Erigeron canadense L. — Transamerican. — Europe (generally), N to N Sweden. 

 Almost cosmopolitan. 



Jiinciis tenuis Will, {macer Gray).^ — N. America (generally), also C. & S. America. 

 — Europe (widely, since before 1850), N to C Sweden. N. Africa. Australia. 



^ For further information, vide Jessen & Lind, 1922-23, Hulten, 1950, Fernald, 1950, 

 and Clapham, Warburg, & Tutin, 1952. 



- Probably originally cultivated in Europe and escaped. 



^ By some students, e.g. Heslop Harrison (1953), regarded as native in Ireland. 



