INSECTS. 



185 



green, and after the first moult, dark green to black. 

 Ventral side slate grey. Head shining black. Twelve 

 broad body segments, upon which are many wrinkles 

 of the skin. 



The sluggish adult is found, during May or August, 

 upon kohl rabi and turnips, mustard and charlock, 

 with its wings folded together. The female, by means 

 of her ovipositor, saws small holes in the margin or 

 under side of the leaf, and lays her eggs in these. 

 The larvse are hatched in from four to six days, and 

 they undergo four moults. The presence of the 

 larvae can be detected by their cast skins, which 

 remain sticking to the leaves even when the animals 



Fig. 91. — The Turnip Saw-fly (^Athalia spinarvm) : 

 adult female and two caterpillars. 



themselves, which are often found rolled up on the 

 under sides of the leaves, cannot be seen. The enemy 

 is also known by its way of feeding, for the larvae 

 keep on the surfaces of the leaves (upper or under 

 surface) and eat out longish holes. As soon as these 

 have reached a certain size, other parts of the leaves 

 or other leaves are attacked. When the larvae are 

 numerous the holes continually increase in number 

 until only the leaf-ribs are left. The mature larvae 

 creep into the soil to a depth of from two-fifths to 

 four-fifths of an inch, and spin a small cocoon. The 

 saw-fly emerges either the same or the following year. 

 These insects may therefore appear in May or in 

 August, but in many cases they are seen at only one 

 of these times, either the summer or autumn turnips 

 being attacked, as the case may be. Memedies .- Fowls 

 and ducks willingly eat the larvae, and, provided they 



