226 THE ENTOMOLOGIST. 



and thus from being solitary feeders they become gregarious; 

 but before this state of things is brought about, the caterpil- 

 lar ceases to feed, shortly afterwards throwing off its skin for 

 the first time, and, like other leaf-mining hymenoplerous 

 larvae, it sheds its skin entire : its body is then spotless. 

 Recovering slightly from the ecdysis, its active little jaws are 

 again in motion, and, whilst thus engaged, its decorative 

 markings slowly unfold themselves, and it is then seen that 

 the plates on the ventral surface of its anterior segments are 

 of a different shape ; for example, the 2nd segment has an 

 oblong shining black plate ; the decorations of the 3rd, 4th 

 and 5th segments are also of the same colour, but they are 

 square in form, and the 6th segment has a minute black cen- 

 tral dot : by and bye the movements of the jaws are observed 

 gradually to decrease, finally ceasing to move. It then enters 

 upon its third stage of larval existence ; after moulting it lies 

 in a quiescent state for a time, and at its expiration its mas- 

 ticatory organs are again seen to be in active operation ; its 

 head then gains a darker tint, and the back of the 2nd seg- 

 ment has an oblong mark, the outlines of which are of a 

 darker hue ; this, in some individuals, is divided down its 

 centre: it 'is, however, on the ventral surface of the little 

 creature's anterior segments that we perceive the greatest 

 change, the 2nd segment then having an irregular-shaped 

 black plate, whilst the 3rd, 4th and 5th segments have a 

 small circular black plate ; the minute black dot previously 

 visible on the centre of the 6th segment having quite disap- 

 peared. Arriving at its adult state, the caterpillar sheds its 

 skin for the last time ; its length is then about five and a half 

 lines, its mouth is dark brown, its eyes black, its head very 

 pale brown, and its body whitish : at this stage of its 

 existence it loses its appetite, becomes indolent, and re- 

 mains in its mined abode for a certain period before descend- 

 ing to the ground, which it enters, and, after forming its 

 cocoon, undergoes its pupal metamorphosis. The parasite 

 which infests this larva, on arriving at its adult state, quits 

 the body of the Tenthredo-larva, and constructs its own nar- 

 row cocoon within the mined birch-leaf. By the 4th of July 

 the larvaj of this Tenthredo reach their maximmu, and ten 

 days afterwards very few of them are to be found feeding, the 

 perfect insects liberating themselves from their cocoons at 



