1 907-1908.] Galls^ Gall-makers^ and Cuckoo Flies. 45 



the larger gall-gnats forms on the willow a cone-shaped gall, 

 in the middle of which it lives, smaller gnats taking up their 

 quarters in the outer portions. Such cuckoo-flies are termed 

 inquilines (Latin, inquilinus, a lodger), and they are probably 

 quite as numerous as the gall-making species. The hymen- 

 opterous genus Synergus consists entirely of inquilines ; they 

 are found in nearly all the different galls of the oak. Peri- 

 clistus is another inquilinous genus of Hymenoptera, species of 

 which are constantly met accompanying the grubs of Ehodites 

 in the mossy bedeguar and other galls of the roses. Some 

 of the gall-flies lodge in the galls of the gall-midges ; other 

 galls occur in which the relationship is reversed. Inquilines 

 do not make galls for themselves, but insert their eggs into 

 the galls formed by other insects. Their larvae generally de- 

 velop more quickly than those of the gall-maker: the latter 

 are in many cases destroyed or ejected by the intruders; in 

 other cases the presence of guest-flies does not afiPect the 

 original occupants. These relations are so closely analogous 

 to those of the cuckoo and the birds in whose nests it lays 

 its Qgg, that inquilinous insects well merit the name cuckoo- 

 flies. The term has unfortunately been appropriated for 

 ichneumons and other parasites, like the ruby-tail which 

 invades the cells of the bee, but the inquilines certainly have 

 a superior claim to the designation. Strangely enough, in- 

 quilines often exhibit an extraordinary outward resemblance 

 to the gall-makers with whom they associate. 



In addition to inquilines, insects of another description are 

 frequently present in galls. Both the gall-maker and its 

 lodgers are eagerly sought after by ichneumon flies, which 

 insert their eggs into the bodies of the grubs within the gall. 

 These parasites are for the most part Chalcidae, small hymen- 

 opterous flies arrayed in bright metallic colours. The species 

 are exceedingly numerous ; both the original occupant and each 

 of its lodgers may be attended by a specific parasite; the 

 latter in turn is persecuted by others. On account of the 

 amount of this rascality prevailing in insect society, the 

 tenants of a gall often exhibit astonishing diversity. All 

 three classes of inmates are occasionally represented in the 

 bedeguar of the rose. The larger galls also contain commen- 

 sals ; these conflict in no way with the gall-maker or inquil- 



