INTRODUCTION 



The beautiful colours, diversity of sizes, and the 

 peculiar shapes of many British oak galls impart an 

 unusual interest and charm to their study. It, how- 

 ever, possesses an additional interest to the student of 

 Natural History. The gall-makers, with the numerous 

 Parasites, Inquilines, and other creatures which 

 emerge from the galls, invite the student to extend 

 his research in another direction, and when he does 

 so Entomology becomes inseparably associated with 

 Botany. 



Collecting'oak galls is a most fascinating occupation. 

 It does not require a greater amount of time than is 

 devoted to gathering material for an herbarium. 



The principal British oak gall-producing insects are 

 the Cynipidge, a family of the Hymenoptera. Flies 

 with two wings, or Diptera, are represented by a few 

 species ; there is also one species of Coccus, and one 

 Funo'us. 



A few species of flies producing galls on other 

 plants, are of medium size. Tephritis hardanse, and 

 UrojjJwra solstitialis, which produce galls in the seed- 

 heads of common burdock, and in thistle stems 

 respectively, are typical examples. The alar extent 

 of these species is about 8-10 mm. But the majority 

 of gall-flies (including those on the oak) are very 

 diminutive, many species not measuring 2 mm. To 

 these the name of gall-gnats, or gall-midges, may 

 appropriately be given. They produce galls in a great 



