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, s6me 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, Cynipidae, 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 Ichneumonidae, Chalcididae, Braconidae, 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 larvae 
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 maybe 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 Cynipidae including the gall-makers, 
and the much smaller family, Figitidae, 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 larvae 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 Cynipidae reference has been made to the division 
into gall-making species and parasitic species, the latter constituting but 
