ARTHROPODA. 147 



a thousand eggs will be found, as in Cynips qtiercus-radicis. Oak- 

 apples are the galls of C. terminalis ; the bullet-galls of the oak, 

 of Cynips Kollari -. and oak-spangles, of C. longicornis. The 

 " bedeguar," or gall of the wild rose, is caused by Bhodites ros&. 

 Cynips aptera form clusters of galls on the roots of the oak. 

 Gall-like substances are also produced by other Hymenoptera. 



In the Terebrantia the larvse resemble the caterpillars of the 

 Lepidoptera, having legs varying from three to eleven pairs, but 

 always six true legs, the remainder abdominal or prolegs. All 

 other Hymenoptera have footless larvse, which are often parasitic. 

 Many species of Hymenoptera spin cocoons. 



To this order belong saw-flies ( TenthredinidcB), the turnip saw- 

 fly (Athalia spinaruin), whose black caterpillar is so destructive to 

 our turnip-crops, ants (Formicidce), the wasp (Vespa vulgar is), 

 hornet ( Vespa crabro), the honey-bee (Apis mellifica), and humble- 

 bees (Bombi). More than 16,000 species are known, of which 

 about 3000 are British. 



Six groups may be distinguished ; the last two or three are fre- 

 quently mentioned as the " aculeate Hymenoptera. 



Posterior segments of the abdomen retractile TUBULIPEKA. 



Posterior segments of the abdomen not retractile. 

 Females armed with a saw or borer. 



Abdomen sessile TEREBRANTIA. 



Abdomen petiolate PUPIVORA. 



Females armed with a sting. 



With wingless neuters HETEROGYNA. 



With winged neuters, if any. 



Basal joint of the posterior tarsi cylindrical FOSSORES. 

 Basal joint of the posterior tarsi dilated ... MELLIPERA. 



TEREBRANTIA. Abdomen sessile, in the female armed with a 

 saw or saws or a borer. Larva with six legs and with a number 

 of prolegs. Feed on vegetable substances. 



By means of the saw or borer the female makes slits or punc- 

 tures in the shoots of young plants or in trees, in which she places 

 her eggs ; galls are frequently the result. A number of species 

 form double cocoons, sometimes of earth, in which they pass the 

 winter. In the TenthredinidiB the female is furnished with a 

 pair of saws, in the Siricidas with a borer. 



TcnthredinidcB. Perga. Fenusa. 



Cimbex. Hylotoma. Selandria. 



Abia, Pachylota. Allantus. 



Trichiosoma. Athalia. Ernphytus. 



L2 



