THE ZOOLOGIST 



No. 222.— June, 1895. 



MOLLUSCA INJURIOUS TO FARMERS AND GARDENERS. 



By F. V. Theobald, M.A., F.E.S., 



Lecturer in Agricultural Zoology to the South-Eastern Agricultural 

 College, Wye. 



Molluscs have received but little attention from an economic 

 point of view, yet they cause a great deal of loss amongst our 

 field and garden crops, as well as being indirectly the agents of 

 serious diseases in sheep, which are often fatal. Curtis, in his 

 * Farm Insects,' refers briefly to Slugs and Snails. Miss Ormerod, 

 in her valuable Reports, also gives a few useful notes regarding 

 Water Snails ; but there seems to be no complete account pub- 

 lished of the injurious species. 



The Mollusca that are injurious to our crops all belong to 

 the two groups, the Helicidce and the Limacidce, both terrestrial 

 in habits. The group which aids in the production of the 

 sheep disease (liver-fluke) is the Limacidce (or Water Snails), 

 molluscs which, although abundant in water, are often found 

 wandering upon land. It is through these Limacidce that the 

 sheep in all parts of the world become afflicted with that wasting 

 disease produced by the liver-fluke. Although they are generally 

 considered aquatic Mollusca, it must be remembered that most 

 of them pass some time upon land, and may therefore be con- 

 sidered amphibious, whilst others scarcely go near the water. 



The Limacidce are found at all elevations. In our own 

 country they are found in and around the mountain tarns of 

 Scotland ; in the Pyrenees, according to Moquin-Tandon, they are 

 found at a height of 1200 metres. Most of the species are slow 

 crawling creatures. Like all Mollusca, they are hermaphrodite, 



ZOOLOGIST, THIRD SERIES, VOL. XIX. JUNE, 1895. R 



