54 THE VARIATION OF ANIMALS IN NATURE 



in Australia did not become a serious pest till about 1895, 

 apparently owing to a definite change in habits (references in 

 Carpenter, 1928, pp. 111-113). Manhardt (1930) records 

 that a beetle, Luperus xanthopus, after stripping all the willows 

 on the banks of the Elbe, made its way inland in large numbers 

 and attacked fruit trees. In some parts very serious losses 

 resulted. In view of what has been recorded as to the forma- 

 tion of biological races, such invasions have some significance. 

 Still more individual aberrations are seen in the genus Vespa, 

 where species normally subterranean sometimes nest above 

 ground and vice versa (see Stelfox, 1930). 



Mollusca. — An octopus (Bristowe, 1931 ; Robson, 1932a) 

 was found eating spiders, though the diet is normally restricted 

 to Crustacea. 



Limax maximus (Taylor, 1907) is usually found in gardens 

 or near houses, but in Ireland is never found in cultivated 

 ground or gardens. 



Reptilia. — Lacerta muralis according to Eisentraut (1929) 

 is found on the shore in the Balearic Islands, feeding on 

 Halophytes because the normal supply of insects and snails 

 is reduced. 



Birds. — The Black-headed Gull (Larus ridibundus) (Lack, 

 1933) sometimes feeds on land in spite of its adaptations to 

 aquatic feeding. The same species (Gray, 1930, p. 170) has 

 been observed flying in a V-formation like geese. This is 

 very unusual for the species. 



The Reed Bunting (Emberiza schoeniclus) (Lack, 1933) is 

 typically a marsh form, but is very occasionally found nesting 

 in typical Yellow Bunting habitats. 



The Great Tit {Parus major) (Darwin, 1884, p. 141) some- 

 times behaves like a shrike and kills small birds. Darwin 

 gives further examples of habit-anomaly on the same page. 



The New Zealand Parrot (Nestor notabilis) (Buller, 1888, 

 pp. 244-5) was originally insectivorous, but relatively recently 

 began to attack sheep. 



The Barbet (Trachyponus emini) (Loveridge, 1928, p. 41) 

 nearly always nests in burrows, but was once found nesting in 

 a tree. 



Mammals. — The African Buffalo (Bubalis coffer) (Elton, 

 1927, p. 145) used to be a diurnal feeder, but after the rinder- 

 pest epidemic of 1890 became a much more nocturnal feeder. 



