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 luciiis] 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 

 ( Buccinum undatum ), the 

 Dog- Whelk (N asset reticosd], 

 and the Purple- Shell (Pur- 

 pur a 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 (Mytilus edulis] 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. 



Fig. 1244. i, Field-Slug (Limax agrestis] ; 2, Black Slug 

 (Arion ater); and 3, a related species (A. empiricorum] 

 with its eggs 4. 



