KEY TO AMERICAN INSECT GALLS 7 



caused by the defonnation of ash and spiraea leaves and showing no 

 trace of mechanical abrasion or injury. Then there are nmnerous 

 galls which develop as a result of continued stimulation by the 

 gall maker itself, a relation evidenced by the fact that in the case 

 of the beaked willow galls producing parasites, we find mostly 

 partly developed galls which present marked differences from those 

 containing healthy maggots. 



This key to American insect galls is an outgrowth of earlier studies 

 of the gall midges and was assembled primarily to facihtate the 

 identification of the numerous galls submitted for name. It gives 

 for the first time, for American forms, a comprehensive survey of 

 the curious plant growths caused by insects and their near allies, 

 the plant mites. With such a guide many amateurs will doubtless 

 be encouraged to enter a charming and delightful field of study, 

 one which may be followed with profit for the child at school as well 

 as by the student of more mature years. The specialist will find 

 herein references to the best accounts of the numerous species listed 

 as well as a summary of American literature, while the many records 

 of host relationships can not be ignored by the biologist and ecologist. 

 The obvious concentration of many forms upon relatively few host 

 plants, especially those with numerous closely alHed species, such 

 as the willows, oaks and goldenrods, and the great diversity of both 

 structure and food habits among gall midges, all suggest interesting 

 lines of study. These relationships are brought out more clearly 

 in a tabulation of the hosts and galls (see page 215), where 1441 

 species are listed, 6S2 being gall midges and 445 gall wasps. The 

 remainder of the plant deformations discussed in this work are 

 produced by a few of the other two-winged flies or Diptera, four- 

 winged flies or Hymenoptera, beetles or Coleoptera, moths or 

 Lepidoptera, and the true bugs or Hemiptera, especially the plant 

 lice and the plant mites or Eriophyidae, the last being represented 

 by 161 species. The deformations, though numerous, by no means 

 exhaust the possibiHties and in the estimation of Mr L. H. Weld, a 

 student of the Cynipidae, nearly one-third, mostly inhabitants of 

 inconspicuous galls, are still unknown. It should also be remembered 

 that extensive regions are comparatively unexplored for insect galls 

 of all kinds. 



There are not only a large number of different species of gall 

 insects but occasionally some become exceedingly abundant; for 

 example, there was, a few years ago, near Albany, a large oak with 

 its smaller branches almost covered with the giant, beadlike swelHngs 

 of the gouty oak gall, Andricus punctatus (fig. 57) , 



