PACKAun.] INSECTS AS ARCHITECTS. 313 



The largest gall we have is made b}'' the Cijnips confluens, 

 found on the scrub oak. It sometimes attains a diameter 

 of two inches. It begins to form as soon as the leaves 

 unfold. It is at first gi-cen and pulpy and has a central 

 kernel in wliicli the maggot resides. When tlie gall is ripe 

 the shell becomes hard and dr}-, and after the fly has es- 

 caped, which occurs in June and again in October, the de- 

 serted shell is often tenanted by wasps. Some galls, as the 

 bedeguar of the rose, are covered with vegetable hairs, and 

 the variety of form in others is very great. On the rasp- 

 berry and blackborr}-, as well as the blueberry, occur differ- 

 ent sorts of galls. All are the result of the sting of the 

 female, which is thought by some to convc}' a poison into the 

 wound, though it is a question whether the egg introduced 

 by the sting or ovipositor docs not act as an irritant body, 

 causing an excessive flow of sap and accumulation of cells 

 resulting in the formation of a tumor. 



Passing by the ichneumon flies, which after all have the 

 best of it, as they are tenants of living homes, supplied with 

 the choicest of food at no trouble and 

 expense to themselves, we come to the 

 cuckoo flies. The Chrysis (Fig. 245) 

 is not a true wasp, but is in some re- 

 spects allied to it. Its integument is 

 very hard and tliick, and beautifully 

 tinted with green and blue and vari- 

 ous metallic colors. When assailed 

 it rolls itself into a ball, in the manner of a pill bug. Its 

 sting is large and exceedingly painful, but not i)oison()Us. 

 Tl.e Chrysis is called a cuckoo fly, as it has the ichneumon 

 trait of living at the expense of other insects. This fly 

 may often be seen flying about posts and hollow stalks of 

 plants, exploring the holes of wasps and bees, wlu're they 

 lay their eggs. The young hatch out some time after the 

 larval bee or wasp, anil then attack the latter, sucking its 



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