110 CRAYFISH AS CROP DESTROYERS. 



Oniscus asellus is omnivorous, eating animal and vegetable 

 refuse. The Onisci thus act as scavengers ; but they also eat 

 fruit, seedlings, and mushrooms, which they seriously damage, 

 especially the soft fruits, as peaches, nectarines, and melons. 

 Greenhouse and hothouse plants suffer severely from their 

 ravages, as also do strawberry plants, the wood-lice eating away 

 at the roots and around the crowns. They conceal themselves 

 in damp dark places, under stones and suchlike, and in crevices 

 in walls. Kotten woodwork is very often filled with them. 

 The eggs, which are numerous, are carried in a pouch in the 

 thorax, the young wood-lice remaining close to the parent for 

 some time. This grey species cannot roll itself up, as we find 

 is commonly done by many of the other species, whilst it can 

 also be told by the antennfB being eight-jointed (fig. 44, d), 

 instead of seven as in Porcellio and ArmcKJilUJium (b). Arma- 

 dillidiuin vulgaris (a) is larger, smoother, and of a uniform 

 slaty-blue, and always rolls up into a ball at the least stimulus 

 (c). Porcellio sraher (b), with the seven-jointed antennfe, is 

 brown and much varied in colour, and with a rough shell and 

 two longish anal spines. There are many species in this genus, 

 but the above are the commonest. All the AVood-lice can be 

 easily trapped by placing pieces of potato or scooped-out apples 

 about. Pots filled with moss and horse-dung invariably attract 

 large numbers, when they can be seen in the day-time and 

 killed. The only poisons I can find to kill them are mercury 

 bicyanide and Voss's phospho-nicotyl. 



Crawjisli as Crop Destroyers. 



In some restricted localities in the south of the United 

 States a crawfish or crayfish does considerable damage. In 

 the Houston clay lands of Mississippi and Alabama certain 

 areas are so infested by these Crustacea that it is almost im- 

 possible to raise any crop with profit. The soil they infest is 

 very Avet, even in dry seasons several feot of water remain in 



