424 THE BIOLOGY OF INSECTS 



and W. F. Fiske, 191 2). It is remarkable that this moth 

 which has become a pest across the Atlantic during the 

 last fifty years has within the same period completely 

 died out as a native species in Great Britain. A remarkable 

 recent success in acclimatising the parasitic enemy of an 

 injurious insect has been achieved by R. J. Tillyard (1926), 

 who has introduced from North America the chalcid 

 Aphelmus fnali, in order to keep in check Schizoneura 

 lanigera the Woolly Aphid of the apple, brought into New 

 Zealand years ago and established there as a pest '* almost 

 unbelievably virulent." After overcoming its first southern 

 winter the Aphelinus has become so well established in its 

 new home that '' the woolly aphis is now under satis- 

 factory control," and consignments of the parasite have 

 been passed on to carry out similar beneficial work in 

 Australia. 



Among the insects that are especially liable to transport 

 from land to land by unwitting human agency are those 

 which live as '* messmates " in dwelling-houses and stores, 

 eating various foodstuffs provided by man, and finding 

 in many haunts such shelter and warmth that they can, 

 even if they come originally from tropical regions, survive 

 and multiply amid suitable surroundings in cooler countries. 

 Many insects of this associative group are, as might be 

 expected, common on shipboard. In a previous chapter 

 (p. 269) attention was called to the flattened body- form 

 of cockroaches, making it as easy for them to shelter 

 in the crevices of a dwelling-house as under bark or among 

 fallen leaves in a forest. The Common Cockroach (Blatta 

 orientalis) of our kitchens is, as its name implies, a native 

 of the eastern tropics ; it has now been established in 

 Europe and Britain for more than a century, and in many 

 districts its spread from larger towns to country villages 

 may be traced ; it seems, not by violent combats but by 

 eflFective competition, to drive out from places which it 

 invades that much older home-mate of European man, 

 the House Cricket {Grylliis domesticus). The smaller and 

 paler German Cockroach (Blattella germanica)^ a later 



