TURNIP SAWFLY. 



197 



fast at pleasure) on each of the succeeding eight segments, 

 excepting the fourth from the head, and another pair of 

 sucker-feet at the end of the tail — thus having only one 

 segment besides the head unfurnished with feet. They 

 greatly enjoy being exposed to the full heat of the sun. When 

 full grown, which is in about three weeks, the caterpillars are 

 from about half to three-quarters of an inch in length ;^ they 

 then go down into the earth, spin a silken cocoon, which is 

 smooth and white inside, but not easily distinguishable from 

 the earth, which sticks to it externally ; and from these 

 cocoons the Sawflies come out in about three weeks in the 

 early summer, and are ready to lay eggs and start a new 

 attack immediately. Later in the season, three months pass 

 before the caterpillars turn to chrysalids, and many of the 

 autumn brood are believed to remain in the cocoons during 

 the winter, and not to change to chrysalids (and thence to 

 Sawflies) till the next spring. 



These flies are very pretty, of a bright orange, with a 

 deeper reddish colour just behind the black head ; the four 

 transparent wings are netted over with veins, and are yellow- 

 ish towards the base ; the legs are stout and short, with the 

 shanks hairy ; and the feet are whitish, with the tips of the 

 joints and all of the lowest joint, as well as the claws on it, 

 black. 



The mischief caused by these flies when they occur in large 

 numbers is simply overwhelming, and often (in such cases) 

 only ceases with the total destruction of the crop, in conse- 

 quence of the voracious appetites of the grubs and the rapid 

 succession of broods.* 



The Sawfly caterpillar feeds on Charlock, Wild Mustard, 

 and other wild plants of the Cabbage tribe. 



Prevention and Eemedies. — The best of these are to be 

 found by looking at the habits of the grubs. 



If these grubs or caterpillars are disturbed whilst they are 

 changing their skins, which happens every six or seven days 

 during the three weeks in which they continue feeding in grub 

 form, they die ; for if they loose hold with the pair of feet at 

 the tip of the tail during this operation they cannot fix them 

 again ; consequently they have nothing they can pull against 

 to drag themselves out of the old tight skin, and therefore 



* For further details of the enormous quantities in which they have been 

 recorded as appearing in various places, the swarms in which they pass from 

 one spot to another, and much valuable information too long to be entered on 

 here, the reader is referred to the account (from which the above note is 

 abridged) given by John Curtis in his ' Farm Insects.' Much information will 

 also be found regarding this attack in ' Mon. of Brit. Phytophagous Hymeuoptera,' 

 by Peter Cameron, pp. 307 — 313, 



