PSYCHE. 



THE DISTRIBUTION OF HOLARCTIC COLLEMBOLA. 



BY JUSTUS WATSON FOLSOM, CHAMPAIGN, ILL. 

 [.\nnual address of the retiring president of tlie Cambridge Entomological Club, January ii, igoi.] 



No less than one hundred and fifty- 

 two species of Collembola are known to 

 occur in North America, of which thirty- 

 eight, at least, are shared with Europe. 

 Their specific identity has been estab- 

 lished, not simply from descriptions, 

 but by a thorough comparison of speci- 

 mens. Twenty-five per cent of the 

 Nearctic species, then, are also Palae- 

 arctic. Specimens of the latter, as a rule, 

 average slightly larger than of the form- 

 er, but that is all. 



I doubt if as large a proportion of 

 Holarctic species is recorded for any 

 other order of animals ; moreover, this 

 proportion is increasing, with the com- 

 parison of additional specimens. 



Apparently restricted to the eastern 

 part of the United States are several 

 species which may have been recently 

 introduced ; such are Neaniira viuscorutn, 

 Aphorura armata, Orchesella cincta, Sim 

 buski, Tomoccrus Tulgaris and tridenti- 

 feriis. 



The following occur abundantly 

 throughout Europe and the United 

 States: Aphorura incrmis, Poilura aqita- 

 tica^ Achonttes armatiis, Jsotonia piiiettirin. 



7'iridis and palustris, also Eiitomobrya 

 multifasciata. These are the more ob- 

 trusive members of the order and, hav- 

 ing been widely collected, furnish 

 valuable data for the study of distribu- 

 tion. The list will doubtless be in- 

 creased when more is known about 

 the Collembola of the western states ; 

 as it is, the forms next named, which 

 range throughout Europe, are known to 

 occur in most of the States east of the 

 Rocky Mountains : Aiiurida granaria, 

 Isotoma (increa, LepidocyrtHS (ya/ieiis, 

 Sira nigromaculata, Stniiithuriis aquati- 

 ciis, malmgreni, hortetisis and elegans. 



In the arctic regions the less special- 

 ized Collembola flourish, some species 

 becoming larger than in middle Europe. 

 Thanks to several expeditions, our 

 knowledge of the arctic range of many 

 species is definite. Of the sixty known 

 species of arctic and subarctic Collem- 

 bola, at least twenty are broadly dis- 

 tributed in tlie United States, and all 

 but a few occur in northern and middle 

 Europe; in fact, but three or four are 

 peculiar to the arctic region. 



In (Greenland. Spitzbergen, Franz 



