NATURE'S • CRAFTSMEN 



or to any other object, and can thus swing free beyond 

 its tube and cairn without being carried away by the 

 current. When from any cause it is set adrift, or vent- 

 ures out of its bounds, these anchor-hooks must be of 

 great use in aiding it to control its course and destina- 

 tion. When it wishes to stop, it has simply to "cast 

 anchor" and hold on with its grapnels. When it wants 

 to move on, it "hoists anchor" and drifts away. When 

 forced out of its domicile, it can move about with much 

 freedom; but in its native waters it probably keeps 

 close to its own castle. 



Net-making caddis worms are numerous in Brook- 

 camp Run, as they doubtless are in most American 

 streams. Nearly every stone within the riffles, or parts 

 where the brook runs rapidly — which are the favorite 

 sites for caddis settlements — has one or more caddis 

 cairns upon it. As one looks down into the water he 

 sees that many of the rocks, pebbles, sunken twigs, and 

 other objects are covered with threadhke streamers, one 

 end of which is free and floats downward with the cur- 

 rent. Most of these are hydropsychid threads, and are 

 covered with fine sediment. When taken from the 

 water they collapse into a mass of slime. Other objects, 

 as the trailing leaves of water-grasses, are similarly 

 covered. 



It is interesting to think how this habit of the caddis 

 to fasten its threads upon rocks, and the habit of the 

 threads to pick up sediment, may have contributed to 

 affect the course of nature. Surfaces thus clogged by 

 this and by other means gradually accumulate refuse 

 of soil, of leaves, of chippage, and decaying matter. 

 Germs of water-plants lodge therein; a rock-garden is 

 formed; more and bulkier matter is assembled. The 



276 



