160 



TENTHREDINIOE OR SAW-FLIES ; TURNIP-FLIES. 



'IG. 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. 



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

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



metamorphosis; but in 

 general the larvae come 

 forth at an earlier 

 period, and feed upon 

 the exterior of the 

 leaves. They greatly 

 resemble the Cater- 

 pillars of Lepidopter- 

 ous insects; but usually 

 y 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 pupas, 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 Athalia centifolice, 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 larvae 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 



