232 SNAILS AND SLUGS [CH. VII 



and the Stapkylinid and Hydrophilid families of beetles 

 all prey systematically upon snails. 



Ants are recorded by Lowe as attacking Helix aspersa, 

 and the larvae of dipterous flies destroy large numbers of 

 gastropod eggs. Ecto-parasites are relatively few, the 

 best known instances being various species of mites (Acari). 

 Of these Conchophthirus and Philodromus live upon the 

 slime of various molluscs, while others inhabit the pul- 

 monary chambers, as also does the Oligochsete Worm, 

 Chcetog aster. The Endoparasites are chiefly the immature 

 Trematode and Cestode flatworms. An account of these 

 will be found in a subsequent chapter (vide pp. 303 316). 

 A Nematode, Ascarioides limacis, is said to occur in the 

 eggs of Limax and in the same slug is found the 

 Gregarine Protozoon Isospora rara. 



Economic uses. Though generally harmful to agricul- 

 tural industries some few gastropods are undoubtedly 

 useful. All species of Testacella are predatory and clear 

 the soil of numerous injurious Nematode worms, coleo- 

 pterous and dipterous larvae, and likewise of their own 

 relatives, the herbivorous slugs and smaller snails. 



As articles of human food snails have long been held 

 in high esteem by many persons. The Romans imported 

 choice varieties and fattened them in snail farms or 

 Cochlearia, providing them with a diet of bran, flour, and 

 herbs, with a judicious admixture of wine dregs. Pliny 

 informs us that Fulvinus Hirpinus made the first enter- 

 prise in snail-farming at Tarquinium about the year 

 50 B.C. 



Varro gives full directions for snail culture in his De re 



