148 



The Galls of Essex ; a Contribution to a 



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fleshy and thick, probably belong to a closely-allied, but 

 distinct species. 



Salix alba, L. Leaf. The margins 

 of the leaves are twisted and consider- 

 ably thickened. This j)seudo-gall is the 

 work of the larva of Cecidomyia clausilia, 

 Bremi. (Fig. 49.) 



Salix alba, L. Terminal leaves. The 

 willow " rose-gall" is too well known to 

 need detailed description, but it is more 

 than probable that we have t^svo or three 

 closely-allied species whose respective 

 galls are not clearly differentiated. The 

 common form is the well-known tuft of 

 terminal leaves or leaf-rosette which is 

 so conspicuous an object at the end of 

 the twigs of our common pollard and 

 other willows, especially so on the bare 

 twigs during winter. The gall consists 

 of an imbricate mass of shortened, sessile, 

 and crowded leaves ; in the centre is a 

 small, hard, inner gall, which contains 

 one or more larvae of the gall-gnat ; the 

 larvae pupate within the gall in spring, 

 and the imagos emerge therefrom in May or June. Ceci- 

 domyia RosARiA, H. Loew. Similar galls occur on S.J'rwjilis, 

 S. Caprea, and other w^illows. 



Salix Capeea, L. Twigs. More or less globular, woody 

 swellings of the twigs of this sallow are frequently noticeable : 

 these are commonly the work of the gall-gnat mentioned 

 below, but more rarely of a sawfly ; these latter most com- 

 monly occur on older twigs than the former. More than one 

 larva occur in the galls ; they pupate therein in thin brown 

 cocoons in April, and the sawflies emerge therefrom in May 

 and June. Cryptocampus pentandr.e, Ketzius. 



Salix Caprea, L. Twigs. The commonly found hard, 

 woody, irregular, and variable swellings of the twigs of the 

 sallow and other willow species are the work of gall-gnats. 



Fig. 49. 

 Cecidomyia clausilia. 



