452 



The Grey Field Slug. 



[Aug., 



1920 was particularly favourable to slugs, and therefore during 

 the past winter many fields of cereals suffered from their 

 attack. The damage to plants was distinctly noticeable in the 

 Bristol district, and examination showed lar^e numbers oi slugs 

 in the soil, beneath clods, under stones', root residues and 

 the like. 



In moist, showery weather, when vegetation is very damp, 

 slugs crawl about on their food plants and feed quite openly, 

 but in the dry weather they feed low down amongst the leaves 

 near the ground, -and in very densely foliaged plants, like 

 cabbage, they get inside the " heart " and feed where it is 

 more moist, and therefore more suited to their requirements. 

 In particularly bad attacks, slugs may tunnel into plants below 

 the surface of the ground; root crops and tubers suffer most 

 in this connection. Instances have been cited where damage 

 to gooseberries and currants has been quite serious; this 

 happens occasionally after continued heavy rains. Though 

 most plants are attacked by slugs, certain weeds seem to be 

 consistently selected as their food plants. These include 

 charlock, cresses, garlic mustard, docks and nettles. 



Description and Life History. — The adult grey field slug 

 varies in colour from pale-grey, through dark-grey to brown, 

 and occasionally yellow. When extended it measures up to 

 2 in. in length; the most common length, however, is IJ in. 

 The tail end tapers off, while the head is blunt and bears two 

 pairs of retractile tentacles. Below, and behind, these tentacles 

 is the mouth, which has a fleshy lip above and a rasping organ, 

 the radula, below. This organ is furnished with a mass of 

 blimt teeth, by means of which the plant tissue is rasped or 

 scraped aw^ay, the vascular strands being left. A short distance 

 behind the head is an irregularly oval mass, the mantle, 

 associated with the small rudimentary shell. The mantle, 

 in which is located the respiratory orifice, is generally darker 

 in colour than the body, above which it is slightly, but 

 distinctly raised. From the mantle to the tail the body has 

 reticulate markings which are less distinct towards the sides. 



The body is rounded above, but below it has a flattened 

 surface, the sole or foot, which is readily distinguished as it 

 is lighter in colour than the body. The sides of the sole 

 are provided with tubercles, the whole structure being 

 distinct from the body which lies above it. A viscous mucus 

 is secreted from slime glands located in the skin. According 

 to Taylor,* the slime is " often clear when crawling but 



" Land and Fresh Water MoUuscs of the British Isles." 



