TWO-WINGED FLIES. 223 



kinds, whether in gardens, woods, or cultivated fields, 

 where they inflict considerable injury. They are 

 mostly very small, and are sometimes called "Midges," 

 indeed many of them are quite microscopic ; such as 

 the wheat-midges, so destructive to wheat. These 

 insects are usually studied in association with the 

 galls, distortions, and deformations of the plants which 

 they inhabit. They are in themselves so tiny and 

 delicate, and so difficult to preserve, that it is fortunate 

 for the entomologist that he obtains so much assistance 

 in the prosecution of his studies from the malforma- 

 tion of the 'foster-plants. The larvae live in preference 

 on living plants, nevertheless some species have oc- 

 curred in rotten wood, and some dwell beneath the 

 bark of trees, or in the cones of firs. Most of the 

 larvae confine themselves to one species of plant, 

 whilst some inhabit the galls of other species as para- 

 sites. Those found under the bark of trees live for 

 the most part in company with other larvae. It is 

 probable that the little orange-larvae which are found 

 so commonly living on the orange Uredinous fungi 

 belong to this group. These little creatures, which 

 resemble small maggots, will be seen crawling over 

 the under surface of the leaves of coltsfoot, when it 

 is infested with its habitual orange rust. All the 

 larvae have fourteen joints, which is an apparent ex- 

 ception from all other larvae, which as a general rule 

 have thirteen. 



Every part of a plant, from the root to the flower 

 and fruit, is subject to their attacks, but each species 

 usually attacks the same part of the plant, and de- 

 forms it in the same way. These deformations are 



