348 



UTILITARIAN ZOOLOGY 



tirely to outweigh their misdeeds. Crows, Rooks, and Sparrows 

 are among the most hurtful forms in Western Europe. Some 

 of the mainly beneficial species are: Thrushes, Starlings, and 

 Chaffinches. 



Injurious Reptiles (Reptilia). — It is only necessary to note 

 that Crocodiles, Alligators, and poisonous Snakes destroy a num- 

 ber of domesticated animals. 



Injurious Fishes (Pisces). — Some of the more voracious 

 freshwater forms, especially the Pike [Esox lucius) destroy other 

 species of greater value, or interfere with the work of fish- 

 culture. Skate and Rays are destructive to oysters. 



Injurious Molluscs (Mollusca). — Forms like the Octopus 



and its kind destroy oysters, 



as also do several species of 



boring sea-snail. Of the latter 



the "whelks" detrimental to 



British oyster - culture are 



chiefly the Common Whelk 



{ Bitcciinim iindatitvi ), the 



Dog- Whelk {Nassa reticosd), 



and the Purple-Shell [Pitr- 



p7ira lapillus). Various North 



American species which do 



harm in the same way are 



popularly known as "drills". 



Cultivated plants of almost all kinds are liable to the attacks 



of various Land- Snails and Land- Slugs (fig. 1244), which are 



probably by far the most injurious of all molluscs from the 



human stand-point. 



Among injurious bivalves the Ship- Worm ( Teredo navalis) is 

 notorious for the way in which it has damaged the timbers of ships 

 and wooden piles. At one time it worked such devastation in the 

 sea-dykes of Holland that serious disaster was threatened. The 

 Edible Mussel iyR'Iytihts ediilis) is sometimes an enemy to oyster- 

 culture, as it may cover up and smother beds of young oysters. 



Injurious Insects (Insecta). — These are so excessively 

 numerous, and at the same time so destructive, that they are 

 the subject of a particularly extensive literature, and constantly 

 engage the attention of many skilled naturalists, especially at the 

 numerous experimental Entomological Stations of America. 



DTlII 



Fig 1244. — I, FielJ-Slug ILim.ix .tsrn-slh : 2, Black Slug 

 {Arioii aUf); and 3, a related species [A. einpiri^oyiiiii) 

 with its eggs 4. 



