EXTERMINATION IN ANIMAL LIFE. 413 



Karotonga by missionaries, and for a time proved a blessing by 

 keeping down the small indigenous Eat which then overran the 

 island. Eats becoming scarce, the Cat took to hunting birds. 

 Some species were soon exterminated, and other birds have taken 

 refuge among the almost inaccessible rocks of the interior. The 

 stillness of the forest is now intolerable save for the hum of 

 insects.*" We may mention the more or less complete extirpation 

 of Eattlesnakes in North America that followed the introduction 

 of hogs. In the Virgin Islands " the land mollusks were com- 

 pletely destroyed by the practice of burning over the land, and 

 only dead shells remain to show their former abundance in that 

 locality."! The most deadly enemy of the Prairie-hen (Tympa- 

 nuchus americanus) is the prairie fire in spring, which destroys 

 every nest within its sweep. According to Mr. E. W. Nelson, in 

 the early seventies in North-western Illinois, the farmers in many 

 places burned the prairies in spring after the Prairie-hens had 

 nested, and often gathered for household use large numbers of 

 the eggs thus exposed.! What the Boers have done to the 

 fauna of South Africa by their annual grass fires can never be 

 estimated, as we scarcely can tell what has been destroyed. The 

 small green Cicadas were very plentiful, and their shrill noise 

 well known, at Sydney. Now, Mr. Le Souef tells us, " the im- 

 ported Sparrows in the neighbourhood of that city looked upon 

 these insects as one of their sources of food-supply, and when 

 they heard their note at once attacked them. In course of time 

 only the quiet ones will survive, or those that sing at night. "§ 

 Aporia cratcsgi, a white Pierine butterfly, is now becoming very 

 scarce in its old haunts in this country. According to Mr. Kirby 

 it is supposed that its disappearance is due to the multiplication 

 of insect-eating birds, a consequence of the Wild Birds Protection 

 Act. || The moth " Loelia canosa has become practically extinct 

 in Britain during the last thirty years," Mr. Tutt remarks. 

 " This is generally supposed to have been due to the drainage of 

 part of Barwell and Wicken Fens, but it was probably partly due 



* W. Wyatt Gill, ' Jottings from the Pacific,' p. 126. 



f Lucas, ' Eep. Nat. Mus. Washington,' 1891, p. 613. 



\ Judd, 'U.S. Dept. Agriculture,' Bull. No. 24, p. 13 (1905). 



§ ' Wild Life in Australia,' p. 245. 



i ' Hand-book to the Order Lepidoptera,' vol. ii. p. 141. 



