60 BRITISH FERNS 



which bore down the remaining midrib and stalk of the frond and 

 eventually pupate in the soil near the caudex. We have never been 

 able to discover this fly, but have been informed that it somewhat 

 resembles a house-fly. The only remedy for this is to cut off the 

 frond some inches below the wilted portion immediately the 

 flagging is seen, thus, of course, removing the eggs and preventing 

 development of the grub. Cases of similar attacks in the late 

 summer have been reported to us, but with us they have been 

 confined to the spring. A tiny black snail, Helix alliaria, so called 

 from its pungent onion-like odour, is sometimes a nuisance, gnaw- 

 ing through the bases of even large fronds, which drop mysteriously 

 and without warning in a very provoking fashion. Fortunately, 

 this foe is not numerous. Slugs and snails generally should be sought 

 for and killed when traces of them appear in the shape of slime ; but 

 Ferns do not appear to appeal to them very strongly. Worms 

 should be turned out of pots, if their casts are seen, as they tend to 

 choke the drainage and sour the soil. Wood-lice should be kept in 

 check as far as possible by destroying them in their haunts under 

 the pots and elsewhere ; but as they are chiefly feeders on dead 

 material they are not nearly so inimical to living plants as the other 

 invaders named. 



