FIG. 383 A, extremity of the abdomen of theSawfly, 

 showing the two saws, c, and their supporters, d, ex- 

 tended ; a, the terminal joint of the abdomen ; and 

 b, the two internal horny sheaths. B, a small por- 

 tion of one of the saws very highly magnified. 



1 60 TENTHREDINIOS^ OR SAW-FLIES ; TURNIP-FLIES. 



ing to the parts injured, which forms the abode of the larva in 

 some cases, during its whole life a ., such, and up to its final 



metamorphosis; but in 

 general the larvse come 

 forth at an earlier 

 period, and feed upon 

 the exterior of the 

 leaves. They greatly 

 resemble the Cater- 

 pillars of Lepidopter- 

 ousinsects; but usually 

 differ from them as to 

 the number of their 

 feet, which are either 

 restricted to six, an- 

 swering to those of 

 the perfect insect, or 



amount to eighteen or twenty-two. In order to undergo their 

 change into the pupa state, they spin a cocoon, either on the 

 earth or on the plants on which they have fed ; but they do not 

 become pupae, until they have been inclosed in this for many 

 months, and only a few days before they come forth as perfect 

 Saw-flies. To this group belongs the Aihalia centifolias, or 

 Turnip-fly, which occasionally appears in this country in such 

 vast numbers as to produce the greatest devastation. The larva 

 is twenty-two-footed, and of a greenish-black colour ; whence it 

 is commonly known by the appellation of the nigger, or Hack 

 caterpillar of the Turnip, to which plant it is chiefly detrimen- 

 tal, by devouring the leaves, and thus totally destroying the 

 crop in an incredibly short space of time. It was especially 

 abundant in the south-eastern counties of England, in the years 

 1835, 1836, and 1837. The appearance of the black larvaa is 

 preceded by that of the imago, a pretty yellow and black 

 insect, which is first seen hovering over the turnip-fields about 

 the middle of May or the beginning of June ; it deposits its eggs 

 in the soft tissue of the leaf, puncturing the cuticle by its ovipo- 

 sitor ; and these are hatched in five or six days. In a few days 



