358 INTRODUCTION TO ZOOLOGY CHAP. 



shortly before the fly emerges. Sometimes numbers of these 

 pupae are to be seen in this position within a few square yards 

 of grass land. It is enabled to move up- 

 wards in this way by the spines which pro- 

 ject from all the abdominal segments, and 

 which are specially numerous near the end 

 of the body. These keep the body from 

 slipping backwards. 



The pupa here, as in gnats and midges, 

 bears on its head two little respiratory horns. 

 When the fly is ready, it escapes through 

 a split along the dorsal exposed part of the 

 thorax of the pupa, and flies off with the 

 Fia. 285. two fore-legs extending forwards and the 

 W u a - f our hi n d_} e pr S stretched out behind. 



a, Respiratory horns. m< i ? ,1 



Tipula okracea is perhaps the commonest 

 Crane-fly. It is to be seen in numbers especially in August 

 and September. 



The Spotted Crane-fly (Pachyura maculosa) is also very 

 abundant, more particularly in gardens. It can be dis- 

 tinguished by its yellow body marked with darker spots. 



These Crane-flies would rapidly become a serious pest if it 

 were not that their numbers are kept in check by rooks, 

 starlings, peewits, and other birds that feed on them. 



Family 5 : CECIDOMYIDAE (GALL-MIDGES) 



One other family of small, insignificant flies belonging to 

 the Diptera Nemocera is worthy of mention, because of the 

 fairly common galls produced by their larvae on different 

 plants. These are known as the Gall-midges or Gall-gnats. 



The flies are minute, and often brightly coloured. They 

 have rather broad wings with very few nervures on them. 

 The antennae are relatively long and hairy. The female has a 

 long ovipositor with which she places her eggs in the tissues 

 of the chosen plant, and around the larva arises a Gall. 



The Hessian Fly (Ceddomyia destructor), which sometimes 

 does great damage in corn-fields, is one of these Gall-midges. 



Another (Cecidomyia taxi) forms a gall at the end of a 

 yew twig, causing the leaves to be clustered in a little bunch 

 (Fig. 286), inside of which is usually one larva only. The 

 gall-midge emerges in June. 



