424 Insect Architecture. 



CHAPTER XX. 



ANIMAL GALLS,* PRODUCED BY BREEZE-FLIES AND SNAIL- 

 BEETLES. 



HHHE structures which we have hitherto noticed have all 

 -* been formed of inanimate materials, or at tha most of 

 growing vegetables ; but those to which we shall now advert 

 are actually composed of the flesh of living animals, and 

 seem to be somewhat akin to the galls already described as 

 formed upon the shoots and leaves of plants. These were 

 first investigated by the accurate Vallisnieri, and subse- 

 quently by Keaumur, De Geer, and Linnaeus ; but the best 

 account which has hitherto been given of them is by our 

 countryman Mr. Bracey Clark, who differs essentially from 

 his predecessors as to the mode in which the eggs are de- 

 posited. As, in consequence of the extreme difficulty, if not the 

 impossibility, of personal observation, it is no easy matter to 

 decide between the conflicting opinions, we shall give such 

 of the statements as appear most plausible. 



The mother breeze-fly (Oestrus bovis, CLARK ; Hypoderma 

 bovis, LATR.), which produces the tumours in cattle called 

 wurbles or wormuls (Quasi, worm-holes), is a two-winged insect, 

 smaller, but similar in appearance and colour to the carder- 

 bee (p. 75), with two black bands, one crossing the shoulders 

 and the other the abdomen, the rest being covered with 

 yellow hair. This fly appears to have been first discovered 

 by Vallisnieri, who has given a curious and interesting 

 history of his observations upon its economy. " After having 

 read this account," says Eeaumur, " with sincere pleasure, I 

 became exceedingly desirous of seeing with my own eyes 



* In order to prevent ambiguity, it, is necessary to remark that the excres- 

 cences thus called must not be confounded with the true galls, which are occa- 

 sionally found in the gall-bladder. 



