HYMENOPTERA 



61 



times, instead of the expected gall insects, a number of very 

 minute Chalcis flies appear. These in their larval stage 

 are parasites on the gallflies (Fig. 59). 



Galls used in the making of ink and tannic acid are pro- 

 duced by a species of Cynips on the oaks of Asia and 

 Europe. A few of the Diptera, many of the Hemiptera, 

 and some of the Arachnida also produce galls. The maple 

 spot gall, so common on the leaves of the red maple, is 

 made by the fungus-gnat (Sciara) of the order Diptera. The 

 conical gall of the witch-hazel is produced by a plant louse, 

 as is also the cockscomb gall on the elm leaves. 



FIG. 45. Blackberry knot 

 gall common on the stems 

 of the blackberry. Nat- 

 ural size. 



FIG. 46. Maple spot gall produced by 

 a fly. 



Fig Producers. The fig insect (Blastophaga grossorwn) 

 is the most valuable member of the gall family, as with- 



