202 NATURE-STUDY REVIEW [12:5— May, 1916 



the gall has attained its full growth, reaching a length of about an 

 inch and one-fourth and a diameter of about an inch. 

 There is, however, great variation in the size of the fully 

 developed galls. Dissection of a gall at this time reveals the fact 

 that the bud has produced from sixty to seventy-five scales which 

 overlap in such a way as to form a cone-like structure. In the 

 center of these protecting scales is a cell-like cavity containing 

 the larva that has hatched from the egg laid within the bud, and 

 has lived upon the tissue of the willow. The larva remains in 

 the gall throughout the rest of the summer and all of the next 

 winter. As spring approaches the larva transforms into a pupa 

 and several weeks later emerges as an adult fly which is known to 

 entomologists as Cecidcmyia strobiloides. 



The life-history of the willow-cone gall-fly is comparatively 

 simple, but the gall that it makes not only lodges and protects its 

 maker, but also serves as a residence for many other insects or 

 their eggs and young. Chief among these are the eggs of the 

 meadow grasshopper. The first scale removed will in mam- 

 cases, reveal the long, slender eggs of this species. There 

 may be from one to eight or ten eggs resting side by side 

 between the scales with their long axes directed like the long 

 axis of the gall. The behavior of the meadow grasshopper 

 in regard to its choice of a gall in which to lay its eggs is 

 worthy of note, since it seems to prefer blackened, weather-beaten 

 galls, probably because their scales are more easily forced apart. 

 It seems likely that this insect's habit of laying its eggs in the 

 gall is of recent acquisition for in some cases the eggs are poorlv 

 placed, even between tightly fitting scales where they are flattened 

 and prevented from developing. From this it would appear that 

 the grasshopper has not learned yet to distinguish the kind 

 of gall best suited to its purpose. 



As we proceed toward the interior of the gall, eggs of different 

 sizes and shapes appear among the scales. One investigator 

 found at least thirty-two species of insects inhabiting these galls. 

 Of these, one was the gall-maker; ten were insects, like the meadow 

 grasshopper, that had acquired the habit of laying their eggs in the 

 gall; these we may call inquilines; sixteen were parasites which 

 live upon either the gall-maker itself or upon the inquilines. or 

 hyperparasites which parasitize the parasites; and five were 



