The human transport of animals across the Northern Atlantic 



209 



Sibinia potentillae . , 

 Sitona griseus . . . , 

 S. hispidulus . . . . 

 S. humeralis . . . . 

 S. lepidus iflavescens) 



S. lineatus 



S. puncticollis . . . . 

 S. regensteinensis . . 

 S. sulcifrons . . . . 

 Tychius picirostris . 



Summarizing, then: to be judged especially fit to survive transport in ballast 

 across the Atlantic and to becoming settled in North America, a terrestrial animal, 

 e.g. an insect, should combine the following six properties: it lives on the ground 

 (terricolous), has no pronounced moisture requirements (non-hygrophilous), pre- 

 fers open ground of a waste-place character (at least it is not halobiontic, salt- 

 demanding), is not dependant on special kind of food (polyphagous), is flightless, 

 and has a parthenogenetic reproduction. The only species of Coleoptera from the 

 English ballast-places filling all these requirements are the four Otiorrhynchus 

 weevils and, sure enough, they all crossed the Atlantic. 



It is of considerable interest to illustrate, in form of a diagram (diagram 5), to 

 what extent the beetles of the ballast places combine the six "favourable qualities" 

 just mentioned, keeping "emigrants" and the remaining species apart. The differ- 

 ence is striking: 73 per cent of the "emigrants", but only 46 per cent of the rest, 

 combine more than 3 of the 6 "favourable qualities". 



A similar calculation has been made for Carabid beetles alone (diagram 6), 

 omitting the mode of reproduction (last column of table 6), because all species 

 are bisexual, but adding the stage of hibernation (according to Lindroth, 1945, 

 1949). This may be regarded as having some influence because the transport of 

 a fuUgrown beetle (above all of a fertilized female) gives the maximum chance for 

 a successful colonization. Most ships in the Newfoundland trade left England in 

 the spring (above p. 162) and constant imaginal hibernators were therefore fa- 

 voured. These make 71 per cent (15 species) of the 21 "emigrants" but 66 per cent 

 (41 species) of the remaining species; only among the latter there are some species 

 (6 in number: Amara convexiuscula, A. equestris, Calathus mollis, Dichirotrichus 

 pubescens, Eurynebria complanata, and Trechus quadristriatus), in which the larval 

 hibernation is practically without individual exceptions. — Of the Carabidae of 



14 — 565597 Lindroth 



