Wasps, Bees, and Ants 475 



is that the morphological character of the gall depends upon the genus of 

 the insect producing it rather than upon the plant on which it is produced; 

 i.e., galls produced by insects of a particular genus show great similarity of 

 structure even though on plants widely separated; while galls on a particular 

 genus of plants and produced by insects of different genera show great differ- 

 ences. The formation of the gall is probably an effort on the part of the 

 plant to protect itself from an injury which is not sufficient to cause death. 



An additional interesting feature in the economy of Cynipid life is the 

 presence in the galls of other insects besides the gall-makers. These others 

 are on two footings, that is, some are guests or commensals, and some are 

 true parasites, either on the gall-makers or on the guests! Curiously, among- 

 both guests and parasites are members of the same family, Cynipid», to 

 which the makers and rightful owners of the galls belong. Others of the 

 parasites may belong to the various well-known parasitic hymenopterous 

 families, as the Ichneumonidoe, Chalcididoe, Braconida;, etc., while others 

 of the commensals may belong to entirely distinct orders, as the Coleoptera,. 

 Lepidoptera, etc. Kieffer (a famous French student of galls and gall-flies) 

 gives the following amazingly large list of commensals and parasites bred 

 from a common root-gall on oak, Biorhiza pallida: Commensals, the larvse 

 of five species of moths, of one fly, of one beetle, of one Neuropteron, and of 

 two Cynipids; parasites, a total of 41 species, bred mostly from the 

 various commensals. 



The guest gall-flies, called inquilines, are often surprisingly similar tO' 

 the species which actually produces the gall. A similar likeness between 

 host and guest exists in the case of the bumblebee (Bombus) and its guest 

 Psithyrus (closely related to Bombus). It may be that the guest species is a. 

 degenerate loafing scion of the working stock. 



The group of gall-flies and their allies is looked on as a superfamily, the 

 Cynipoidae, in the latest authoritative classification (Ashmead) of the Hymen- 

 optera, and divided into subfamilies, the C\'nipidas including the gall-makers, 

 and the much smaller family, Figitidas, including the parasitic species. Only 

 about a score of parasitic Cynipoids are yet known in this country, while 

 over 200 gall-making species and inquilines, or guest species, are known. 



To collect gall-flies the galls should be gathered especially in the 

 autumn, for with the end of the growing season the larva; are mostly full- 

 grown and ready to pupate. They should be separated according to kind,. 

 those of each kind being put into small closed bags of fine-meshed bobinet 

 or tarlatan. In these the various gall-flies, inquilines, commensals of other 

 orders, and the parasites will issue, and may be thus identified with their 

 proper gall. 



In the account of the Cynipidaj reference has been made to the division 

 into gall-making species and parasitic species, the latter constituting but 



