THE HESSIAN FLY. 57 



worm hatches, and again makes its short journey to its future 

 home, at the hase of the sheath ; it consequently now nestles at 

 the first and second joints of the young stalk, and is sometimes, 

 though rarely, as high as the third joints. Even before the 

 worm reaches the base of the sheath, it has frequently grown 

 nearly to its full siee, (as shown Fig. m., para. 78.) The stalk 

 has now attained such A^igour and hardiness that it is seldom 

 destroyed by this spring attack. A slight swelling immediately 

 above the joint, (Fig. B §§) commonly indicates the presence of 

 the larva beneath." 



39. " This is afact which has been overlooked, or at ieastnot dis- 

 tinctly stated by writers hitherto. "We only find it noticed by 

 Mr. Bergen, (Cultivator, VIII, 133,) who informs us that in a 

 crop of barley which was destroyed by the Hessian fly, many of 

 the stalks were 'at the joints, as thick as a man's finger.' 

 The insect is, therefore, a true gall-fly, although when but one 

 larva succeeds in reaching the joint, the swelling caused by it is 

 little if at all apparent. More commonly, however, the straw 

 becomes so weakened that it is imable to sustain the weight of 

 the wheat-head, and it accordingly bends down (as represented, 

 Fig. B ft,) with the force of the wind and rains. The appear- 

 ance of a badly infested field, as harvest time approaches, can- 

 not better be described than in the words of M. Koliar. The 

 grain looks as though a herd of cattle had passed through it, so 

 broken and tangled together is the straw. The worm attains its 

 growth and enters its flax-seed state about the first of June, and 

 the flies of this second generation come forth about the last of 

 July, and in August." 



Parasites. 



94. The excessive multiplication of all kinds of insects is pro- 

 videntially kept within bounds by a well known law, which 



