HYMENOPTERA OAK GALLS. 159 



dant on oak bushes and young trees. This gall is now widely dis- 

 tributed over the British Isles (fig. 15G). It is often called the Devon- 

 shire gall, from the fact of its first appearing in that county and 

 causing great alarm. 



The galls are from f inch to 1 inch in diameter, and, as a rule, 

 almost a perfect ball. In some cases two galls coalesced, but in the 

 centre one grub may only be found. As a rule, the gall may be 

 perfectly smooth, but in some cases it is warty. At other times they 

 may be found dwarfed in size and shrivelled, but when such is the 

 case they are generally chambered, and inhabited by parasites, thus 

 contrasting with the true larval chamber, which is normally single 

 and smooth. 



The fly appears at various times, according to locality, from the 

 latter end of April to beginning of June. As the fly is very easily 

 hatched out, and being of a fairly large size, the following detailed 

 description from Adler and Stratton may be given viz. : 



"Fly. Length 4 to 6 mm. ; whole body reddish-yellow; looked at 

 from above, the head appears widened behind the eyes ; cheeks half 

 as long as the eyes, without wrinkles ; antennas filiform, thirteen- 

 jointed, second joint longer than thick, third.goint the longest, twelfth 

 and thirteenth joints partially united. Thorax brown, covered with 

 short hairs ; parapsidal furrows complete ; scutellum with two thickly 

 haired foveas at its base ; metanotum black, vertical, overhung by the 

 scutellum. Abdomen smooth and shining ; second segment covering- 

 half the dorsum, very dark above, with two large hairy spots ; the 

 other segments fringed with silky hairs. Ovipositor long and spiral. 

 Venter exposed. Wings as long as the fly, hyaline, finely haired ; 

 radial cellule open at the margin, elongate, with the areolet opposite 

 its base ; basal abscissa of the radius angled ; cubitus opposite to, but 

 not reaching, the middle of the transverse basal nervure ; legs yellow, 

 margin of the fore tibia? fringed with short depressed hairs ; hind 

 cox* broad j claws bifid." 1 



Synoptical Table of Oak Galls. 



With a view to readily ascertain the name of any gall, it may be 

 considered advisable to arrange them according to the respective parts 

 of the oak-tree on which they may be found. 



1 Adler and Stratton, p. 164. 



