66 BRITISH GALLS 



filicina. The roll is cigar-shaped and shining black at 

 maturity; it contains a single pale orange-yellow larva, 

 which pupates in the earth. This gall has a wide range 

 in Europe and the British Isles. An allied species, Perrisia 

 pteridicola Kieffer, causes a similar gall on Bracken in 

 Germany and Central Europe, but has not as yet been 

 observed in this country. The hypertrophy is feebler ; the 

 larvae are gregarious and colourless. 



The larvae of Perrisia terminalis, perhaps better known to 

 English dipterists under the name of Dasyneura terminalis, 

 cause swollen brown galls in the apices of the shoots of the 

 White Willow and the Crack Willow (Plate VIII., Fig. 4). 

 As many as thirty of the reddish larvae may be found in a 

 single gall, which is formed by the rolling together of the 

 terminal leaves, which also become thickened and brown. 

 The larvae pupate either in the gall or in the earth. 

 Fig, 6 gives a magnified view of a pupa from the gall 

 shown above it, and Fig. 5 thte elegant little fly, highly 

 magnified, the expanded wings of the insect measuring only 

 3%- inch from tip to tip. This gall is frequent wherever 

 S(dix fmgilis occurs. The illustrations are from specimens 

 I gathered in a garden in Gower Street, London, in July, 

 1910. 



Perrisia marginem-torquens causes the margins of the leaves 

 of the Osier and other Willows to become more or less 

 tightly rolled inwards. The roll often extends the entire 

 length of the leaf, and consists of an aggregation of little 

 yellow or reddish pockets, each about 3 mm. long, and each 

 containing a single larva. The gall of P. Inchbaldiana is 

 similar, but is bent like a bow and smaller at each end. 

 Though usually gregarious, these galls are rarely coalescent, 

 and the margin is never continuously rolled. 



Other well-known galls on Willows are caused by gall- 

 gnats of the genus Rhabdophaga. R. saliciperda causes 

 hypertrophy of woody tissue on branches up to 4 inches in 

 diameter. When numerous, as they often are, these galls 

 collectively form an elongated spindle-shaped (fusiform) 



