HYMENOPTERA — OAK GALLS. 



155 



very often be found by workmen when trendiing or uprooting trees in 



winter. They are of a cotfee-brown colour, and vary in size, but the 



average is about the bulk of a common pea 



(fig. 153). They are generally procured in 



■clusters, which very much resemble the honey- 

 combs of the moss-bee, Bomhus muscorum. 



Adler says that, after many observations, he 



found that the flies issue in December and 



January, but adds that other observers found 



the time of their appearance rather variable. 



This last remark 1 can quite endorse, inas- 

 much as galls found by workmen in February 



■did not hatch until well on in spring. In 



this case there is no mistaking the species or 



confounding with parasites, inasmuch as the 



specimens are all apterous. 



The fly varies in size from ■! to 7 



mm. long, wingless, with a rather slender 



thorax. The form is somewhat spider-like, 



and the whole body of a uniform brownish 



colour. 



With regard to the alternate form, Adler 

 made many observations, and found that the 



eggs deposited by Biorhiza uptera result in the formation of the 

 well-known oak-apple. 



Adler watched the egg- laying process very closely, and found that 

 the insect did not de- 

 posit the egg immed- 

 iately after making the 

 incision, but acted on 

 the principle of " one 

 thing at a time," inas- 

 much as she carefully 

 pricked the buds and 

 then returned to deposit 

 the eggs in previously 

 prepared channels. In 

 this way he found that 



on January 27, 1878, the fly deposited 582 eggs during 87 hours. 

 Towards the end of May these galls were fully developed oak-apples. 



15-2.~G-f'?so/Dryo- 

 phaiita divisa. 



.—Ckdh 0/ Biorhiza apterf 



