VEGETABLE GALLS 



761 



GALLS OF RHODITES NERVOSUS ON WILD ROSE LEAF 



in mam' parts of Scotland : and its best- 

 known popular title is the " ]\Iarble Gall " 

 — a name which aptly describes its 

 appearance. 



The Marble Gall-fly is slightly less than 

 one-sixth of an inch in length — that is. 

 from the front of its head to the end 

 of its body. As Gall-flies go, it is a large 

 species. After many fruitless attempts, I 

 succeeded in obtaining a magnified photo- 

 graph from life of this insect. It is seen 

 resting upon the summit of its gall, close to 

 the hole which it has 

 bored in order to escape. 

 The photograph gives a 

 good idea of the strange 

 " humpy " form of the 

 tiny insect ; while the 

 relatively ample wings 

 {they are about 11 milli- 

 metres, or not much 

 under half an inch, from 

 tip to tip when extended) 

 are well indicated. 



I have already said 

 that the Marble Gall-fly 

 is, perhaps, the most 

 curious of its kind. This 

 estimate is based largely 

 upon the well-nigh in- 

 credible fact that every 

 specimen which has ever 

 been seen by naturalists 



has proved to be a female. En- 

 thusiasts in the past have col- 

 lected many hundreds of the galls, 

 and examined carefully each in- 

 sect that emerged from them. 

 But the result of these researches 

 has always been the same. Not 

 a single male has been found. 

 Indeed, it is scarceh' too much to 

 affirm that no male of the species 

 exists ; that it has become totally 

 extinct. 



Now, as this Gall-fly is known 

 to comj)lete only one genera- 

 tion in the year, it is at least 

 conceivable that the species 

 may, in times past, have been 

 " double brooded," producing a 

 sexual generation in alternation 

 with the agamic one. Still allow- 

 ing our imagination to wander, we 

 may suppose that for some reason 

 quite outside our knowledge, the 

 sexual generation became obsolete, leaving 

 the "lone ladies" of the agamic brood to 

 perpetuate the species. Such a supposi- 

 tion would serve to explain in some mea- 

 sure the amazing state of things which 

 at present obtains. But I must warn the 

 reader that we are now wandering quite 

 outside the region of ascertained fact. All 

 that we really know is that this strange 

 GaU-fly continues year after year, one 

 generation succeeding another, and yet no 

 male individual is known to exist. 



GALLS OF KHODllES EGLAMEKlAi ON WILD KOSE LEAF 



97 



