Galls caused by the larvae of Cecidomyia pteridis Mull. 



on 



the secondary pinnae of Pteris aquilina Linn. 

 PLATE 83. 

 Synonymy of Insect. 



Cecidomyia filicina Kief. 



„ pteridis Theobald. 



Habitat of the Common Bracken. — This easily recognised 

 plant is exceedingly abundant in woods and thickets, on 

 heaths and waste places, throughout the whole of Britain. 



The Gall is formed by the larva causing the secondary 

 pinnas to thicken slightly and form a torpedo- or cigar- 

 shaped roll. 



Position. — On the under surface of pinna. 



Manner of Growth. — Gregarious ; sessile ; glabrous ; glossy. 



Colour. — Green, changing to red, finally black. 



Average Dimensions of a Mature Specimen. 

 Length, 5 mm. ; girth, 6 mm. 



May be sought during the months of June, July, and August. 

 The Growth is complete by the end of July. 

 The Typical Condition of the gall is unilocular and unilarval. 

 The Larva pupates in the ground. The imago emerges 

 during the spring. 



Although these galls may be detected when the fronds of 

 the bracken are viewed from above, the quickest and simplest 

 manner of finding them is to lie on the ground under the 

 bracken, and examine the fronds from below. The little rolls 

 are torpedo- or cigar-shaped. They grow rapidly. In some 

 localities they are plentiful, in others very scarce. The largest 

 number the author has found on one pinna is twenty-five. 

 The imagines are difficult to rear. 



The illustration is of specimens gathered at Hastings by 

 the author. 



