36 BRITISH GALLS 



sap-supply, and these provide the requisite shield for the 

 helpless larvae during the long months of winter. 



Oak galls are remarkably sporadic in their times qf 

 appearance. A gall may be very abundant one year, very 

 scarce the next, and perhaps for many successive years. 

 Of course, infrequency of the galls does not necessarily 

 imply scarcity of the insects : they may have been as 

 numerous as ever. In the case of spring forms, atmospheric 

 conditions may retard the rise of the sap, and the larvae 

 perish. Adler states that he was compelled to attribute to 

 meteorological conditions a most important influence over 

 the development of the egg. In 1904 the currant gall 

 was extraordinarily abundant around Ilaslemere. I then 

 recorded in my notebook that " on nearly every Oak tree 

 the male catkins are festooned with them, but here and 

 there a tree may be found which, to all appearances, has 

 entirely escaped attack. We always find exceptionally fine 

 galls on Q. sessiliflom. The catkins which do not bear galls 

 wither up and drOp very quickly ; the stalk of a galled one 

 maintains its vitality for a considerable time." The currant 

 gall is well named. It appears in the latter part of May 

 and early in June on the staminate flowers, and at maturity 

 exactly resembles a red currant (Plate V., Fig. i). 



Fig. 2 on Plate V. depicts a magnified section with 

 the larval cavity. These galls grow with great rapidity. 

 The wasps develop with equal rapidity, and by the end of 

 June the majority will have left the galls. The wasp 

 known as Nemoterus baccamm (Fig. 3) is about 4 mm. long ; 

 the male has fifteen joints to each antenna, his partner one 

 less. The galls also appear on the leaves, in which position 

 they are larger, and green, never red. Barrett noted that 

 the Tortrix Sciaphila communana lives in these galls. Many 

 jjarasites have been bred from them. Rolfe found currant 

 galls on nine species of Oak in the Quercetum at Kew. 

 The female N. baccantm attacks the vmder surface of young 

 Oak leaves, causing the well-known common spangle gall 

 (Plate v., Fig. 4, a, a) to appear in July. These galls are 



