Observations or the T'urnip Saw-Fly. 



387 



A female will lay from 250 to 300 eggs ; and they liatcli in 

 from five to eleven days. 



The black caterpillars are about one-tenth of an inch long at 

 first, but three-quarters, and sometimes nearly an inch in length 

 when arrived at maturity. 



They change their skins thrice during their lives, which extend 

 to nineteen days, or three weeks. 



Previous to changing their first skin they have the power of 

 emitting a thread from their mouths, and are difficult to shake off : 

 after the first moult they fall down on the slightest touch, and lie 

 curled up. 



If the caterpillars be disturbed whilst moulting they die. 



They descend into the earth and there form a cocoon, in which 

 they change to pupae, often lying in the ground the whole winter ; 

 but in summer the saw-flies hatch in three weeks. 



When they descend into the earth, if it be fresh and moist, it 

 is better suited to their economy than when it is very dry. 



Light soils seem to suit them best. 



Swedes by the side of white turnips often not touched : in 

 other instances they have suffered equally. 



Sivedes more or less infested^ but not a caterpillar to be seen 

 on the English turnips. 



The young larvas are fastidious ; and when feeding on an old 

 leaf do not relish a young one. 



They are most voracious immediately after changing their 

 skins ; and when nearly full-grown do the most mischief. 



They do not appear simultaneously ; and there are often three 

 broods in a year. 



A thunder-storm destroyed myriads of the black caterpillars. 



Coldj checks their progress, and often kills them ; and ivet 

 causes diarrhoea, which carries off great numbers. 



Checked and destroyed in the ground by the frost of January, 

 1838. 



Sometimes attack fields in patches; at others commence on 

 one side, going regularly forward ; and again leaving, perhaps, a 

 space in the middle and all the borders untouched. 



Large and open fields more liable to be attacked than small 

 and enclosed ones. 



Rooks and siccdlows are very serviceable in thinning their ranks, 

 the former feeding on the caterpillars, the latter upon the saw- 

 flies. 



The caterpillars seem to be nearly free irom parasitic enemies. 



The streicing of quick-lime, coal ashes, and soot has been 

 attended with various success, and generally v»'ith beneficial results. 



Repeated rolling has killed and checked the caterpillars ; but 

 its effects are partial. 



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