Galls caused by the larvae of Nematus gallicola Steph. 



on 



the leaves of Salix fragilis Linn. 



PLATE 111. 

 Synonymy of Insect. 



Cynips caprea Linn. 



Nematus gallicola Cam., Andre. 



vallisnieri Htg., Thorns., Miiller., Br. and Lad. 



Pontania vallisnieri Costa, Swam, Reau., Roes., Ratz. 

 Habitat of the Crack-willow.— This willow is widely 



distributed over Britain, preferring damp places, by the 



sides of streams and marshes ; it will also grow in woods 



and hedges. 

 The Gall is formed by the accumulation of .'^ap around 



the ovum during the development of the leaf 

 Position. — Along the edges and either side of the mid-rib, 



but not on it. 

 Manner of Growth. — Equal proportions on cither surface 



of the leaf 

 Colour. — At first green, later deep red above, green or pink 



beneath. 

 Average Dimensions of a Mature Specimen. 



Length, 12 mm. ; breadth, 6 mm. ; thickness, 8 mm. 

 May be sought during the months of May to October. 

 The Growth is complete by the end of July (first brood). 

 The Typical Condition of the gall is unilocular. 

 The Larva pupates in the earth. The first brood emerge 



during May, the second during August and September. 



These galls appear to be common everywhere that Salix 

 fragilis occurs, and oftentimes is excessively abundant locally. 

 They are popularly known as " Horse-bean galls," because of 

 the shape and resemblance. 



The gall is al-^o figured by Cameron, " British Phytophagous 

 Hymenoptera," vol. i., plate 3 ; Mosley, " Naturalist's Journal," 

 April, 1898. 



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