PACKARD.] IJNSECTS AS ARCHITECTS. 311 



the exception of the Termites, present such evidences of 

 mechanical skill as the bees and wasps and ants. The 

 Hymenoptera, of which they are the most familiar examples, 

 were among the latest insects to appear on the surface of 

 the earth. The lower forms, so far as the scanty records 

 show, appeared first in the Jurassic rocks, while the ants are 

 first found in the amber of the Tertiary period, so that the 

 ants and wasps and bees were in all probability among the 

 latest insect creations. This inference is borne out by 

 the fact that the individuals and species are ver^' abundant. 

 Did they belong to an ancient stock their numbers would 

 have been thinned out. 



The lowest hymenopterous insect which lives in a house 

 of its own, not, however, made with its own hands, is a kind 



Fig. 243. 



Clothes M'-th. 



of saw-fly (Euura), which constructs a gall. The female 

 la^'s an egg in the bud of a willow ; the presence of the egg 

 sets up an irritation, causes an unnatural enlargement of the 

 bud-leaves, until a round swelling or tumor is formed, in 

 which the false-caterpillar lives and feeds on the walls of its 

 house, which grows with its growth. Mr. Walsh has studied 

 these gall saw-flies. The gall in which Euura orbitalis lives 

 is at first a bud v/hich is enlarged two or three times its 

 natural size l»c'fore it unfolds in spring. In the autumn it 

 bores through the walls of its dwelling, and descends to the 

 ground, burrowing an inch deep below the surface. Here it 



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