302 



MOLLUSCA. 



The following snails have been brought to the author's notice 

 as being very injurious : The Garden Snail {Helix aspersa), the 

 Wood Snail {H. nemoralis), the Strawberry Snail {Hygromyia 

 rufescerm), H. vinjata, and H. capemta, which migrate from the 

 Downs to the fields in numbers at certain times. 



The Garden Snail {H. aspersa), fig. 176, is one of the common- 

 est and most easily obtainable. This large species needs no 



description, as it is well 

 known in every garden. 

 The ova are laid in heaps 

 of sixty to seventy in the 

 earth; they are white, shin- 

 ing, globular bodies, which 

 hatch out in fifteen days if 

 kept in the damp. The 

 young are almost colourless, 

 the shell being thin and 

 transparent. Drought and 

 cold are erroneously considered harmful to snails. At the ap- 

 proach of winter they collect together, and exude a slimy matter 

 which hardens and closes the aperture of the sheik This cov- 

 ering or lid is called the epiphragm, and must not be mistaken 

 for a permanent operculum. The common snail may be found 

 liibernating together in crevices in walls, in old trees, and under 

 rubbish, united together by the agglutinated slime. 



H. ncDiiiralig, or the "Wood Snail, is abundant in hedgerows 

 and upland pastures, especially clover, where it often does much 

 damage. Hygromyia rufescens, the Strawberry Snail, often does 

 much damage to strawberries. 



In destroying slugs, we must bear in mind the fact that they 

 exude a thick slime which retains any poisonous substance we 

 may put over them, and which they can cast off. They cannot, 

 however, repeat the violent excretion of the repellent substance 

 more than twice, so that three dressings at short intervals are 



Garden Snail (Helix 

 Reduced ^. 



