34 BRITISH GALLS 



Some of the galls caused by species in which the alterna- 

 tion of generations occurs are delineated in Plates IV., V., 

 and XXII. 



The first of these concerns the familiar " Oak-apple." If 

 the reader visits a coppice in January, and carefully removes 

 the earth from around some of the roots of an Oak, he may 

 find upon them hard, brownish, spherical excrescences, 

 ranging up to | inch in diameter. All Oaks do not bear 

 them, and perhaps considerable patience will have to be 

 exercised before any are found. These galls may Occur 

 either singly or in large masses as seen in Plate IV., Fig. 5, 

 but are never truly coalescent. If one of them is cut open, 

 a yellowish-brown " fly," about 6 mm. long, will crawl out 

 (Fig. 8). " Fly " is the term in general use, but it is not 

 correct ; the insect is a wasp, not a fly. Figs. 7 and g show 

 respectively the gall and the insect, the latter magnified. 



This wasp is the Biorrhiza aptera. It is always a female 

 and always wingless. Her lot in life is not cast in easy 

 lines. First of all she has to bore through the hard wall of 

 the gall, next she has to push her way up through the earth 

 and gain the trunk. Up this she crawls, a journey beset 

 with a thousand perils. It is winter-time, and, with 

 diminished food-supply, trunk-haunting birds, such as tits, 

 nuthatches, and creepers, are maintaining a very vigorous 

 search for insects of all kinds. Her quest is suitable 

 terminal buds, in which she bores canals and deposits her 

 eggs. Adler has given a vivid description of these boring 

 operations, which differ from those of other gall-wasps. 

 The necessary canals are first bored or pricked in the bud ; 

 the eggs are pushed in afterwards. They are laid, not 

 singly, but in hundreds, and their deposition requires time. 

 "On January 27, 1878," wrote Dr. Adler (I am quoting 

 from Dr. Straton's well-known translation), " a fly was put 

 upon a little oak, and soon began to prick a bud ; when it 

 had finished the first bud, it went on, without interruption, 

 to another, and was altogether eighty-seven hours busily 

 employed in laying its eggs. In these two buds I counted 



