546 



HYMENOPTERA. 



icine, are caused by the punctures of the Cyrdps gaEm 

 tinctorice on a kind of oak growing in the western part 

 of Asia; and. the insect may often be found in those which 

 are not pierced with holes. Some galls contain only a 

 single insect, lodged in a little cavity in the centre; other 

 kinds are inhabited by several grubs, each in a cell by 

 itself, and the cells not unfrequently resemble numerous 

 small seeds, clustered together in the middle of a fruit. 

 Two or three different kinds of insects are often found to 

 come from one gall, namely, a few gall-flies, which are 

 the lawful proprietors thereof, and more numerous four- 

 winged flies (Chalcidid.e), with elbowed- antennas. The 

 latter are bred from grubs, which devour the grubs of 

 some of the gall-flies, or starve them by eating up their 

 food, and thereby contribute to check the too great increase 

 of the gall-flies. 



The largest galls found in this country are commonly 

 called oak-apples. They grow on the leaves of the red 

 oak, are round and smooth, and measure from an inch 

 and a half to two inches in diameter. This kind of gall 

 (Plate VIII. Fig. 9) is green and somewhat pulpy at 

 first, but when ripe it consists of a thin and brittle shell, 

 of a dirty drab color, enclosing a quantity of brown spongy 

 matter, in the middle of which is a woody kernel about 



as big as a pea. A single grub 

 (Fig 253, magnified) lives in 

 the kernel, becomes a chrysalis 

 (Fig. 254) in the autumn, when 

 the oak-apple falls from the tree, 

 changes to a fly in the spring, 

 and makes its escape out of a 

 small round hole which it gnaws 

 through the kernel and shell. This is probably the usual 

 course, but I have known this gall-fly to come out in Octo- 

 ber. The name of this insect is Cyrdps confluens.* (Plate 



* Diplolepis cohflwnttis of my Catalogue, and so named by Mr. Say. 



Fig. 253 



Fig. 254. 



I 



