204 Insect Architecture. 



of the hollow of a wheat -straw or a crow-quill, and equally 

 smooth and uniform. Now the materials being small stones 

 full of angles and irregularities, the difficulty of performing 

 this problem will appear to be considerable, if not insur- 

 mountable : yet the little architects, by patiently examining 

 their stones and turning them round on every side, never 

 fail to accomplish their plans. This, however, is only part 



Stone Nest of Caddis- Worm. 



of the problem, which is complicated with another condition, 

 and which we have not found recorded by former observers, 

 namely, that the under-surface shall be fiat and smooth, 

 without any projecting angles which might impede its pro- 

 gress when dragged along the bottom of the rivulet where it 

 resides. The selection of the stones, indeed, may be ac- 

 counted for, from this species living in streams where, but 

 for the weight of its house, it would to a certainty be swept 

 away. For this purpose, it is probable that the grub makes 

 choice of larger stones than it might otherwise want ; and 

 therefore also it is that we frequently find a case composed 

 of very small stones and sand, to which, when nearly 



Sand Nest balanced with a Stone. 



finished, a large stone is added by way of ballast. In other 

 instances, when the materials are found to possess too great 

 specific gravity, a bit of light wood, or a hollow straw, is 

 added to buoy up the case. 



Nest of Caddis- Worm balanced with Strawi. 



It is worthy of remark, that the cement, used in all these 



