FARM PESTS 41 



and glittering, glassy wings. A sketch of it has been 

 included among the Hymenoptera in the last chapter. 

 It lays an egg in the Corn Fly Maggot's body, and its 

 larva feeds upon and finally destroys its host, thus per- 

 forming a most useful service. (See Plate 3.) 



We now come to the Hessian Fly {Cecidomyia des- 

 tructor) which attacks wheat, barley and rye, the wild 

 foods being couch and timothy grass. In all these cases 

 we shall find that there is a wild alternative food plant, 

 and should therefore time our weed offensive at the 

 most awkward period for the pest, say just when the 

 eggs are hatching, and again when the larvae are half- 

 grown. The Hessian Fly, although only jV ^^^^ 

 long, is a cousin of the Crane Fly or Daddy-long- 

 legs, thus showing that size is no criterion as to relation- 

 ship in the insect world. It is dark in colour, with 

 reddish abdomen, and black or smoke-coloured wings. 

 The eggs, which are red and glossy, are laid in the furrows 

 of the top surface of the leaf-blade, and the maggots, 

 which are legless, yellow in colour, feed between the 

 leaf-stem and the blade. The plants thus become weak- 

 ened from loss of sap, the stems being often " elbowed." 

 The full-grown maggots pupate where they feed, and 

 the white pupse are enclosed in a reddish-brown case, 

 which may be seen sticking out at the leaf -joints and 

 are then known as " flax-seeds." It will be necessary to 

 burn straw where a bad case of Hessian Fly has occurred. 

 The crop that follows should be clover, on which Hessian 

 Fly cannot feed. This insect as a matter of fact has 

 not given much trouble in England of late years, but 

 is always Hkely to turn up in full force. 



The Wheat Midge {Cecidomyia tritici) is closely allied 

 to the last insect, and similar in appearance, being if 

 anything more injurious. A drawing is shown to illus- 

 trate the difference between the two. It will be seen 

 that the wings of the Hessian Fly are hairy and smoke- 

 coloured, whilst those of the Wheat Midge are clear and 



