LIFE-HISTORY OF CADDIS-FLIES 237 



of caddis-flies exhibit distinctive workmanship. Leaves 

 and sticks, stones and shells, or sand alone, are worked 

 up into cylindrical or curved tubes. The binding 

 material is silk spun from the silk-glands and worked 

 up by the lower lip of the animal. Some larvae that 

 live in running water spin a roomy case of silk open 

 at each end and moored to surrounding objects by 

 threads. These threads form a snare in which other 

 larvae become entangled. The caddis, aroused by the 

 increased agitation, emerges from its retreats and kills 

 its prey. 



When the time of pupation arrives, the caddis 

 larva proceeds to add further protective measures. 

 It remains in the case, but closes up the two ends with 

 plates of silk ; or it may block up the openings with 

 stones, or construct a shorter case of stones to replace 

 a leafy one, or other more complex contrivances. 

 Within this shelter the larval skin is shed by the 

 following day, and the pupa appears. In this stage 

 the wings, legs, antennae, eyes, and other organs of the 

 fly are visible, since they lie free and are not glued 

 down, as in the pupae of most moths. But the body 

 is not at rest. It still carries out the undulating 

 breathing movement that we have seen in the larva, 

 and it still possesses the gills. In addition to these 

 processes the pupa has a pair of strong-toothed hooks, 

 or mandibles, quite different from those of the larva. 

 With these hooks the pupa works its way out of the 

 stony case that has protected it and either floats, 

 swims, or crawls to the surface of the water, out of 



