82 



ELEMENTARY LESSONS ON INSECTS 



(b) The shelter tube, built in a crevice lined with silk, 

 to the surface of which sand grains and bits of 

 tissue may be attached, its front end opening 

 into the bottom of the net. 



(c) The larva, with brown 

 head sometimes visible in 

 the bottom of the net, re- 

 treating well inside when 

 disturbed by means of a 

 pull on its draghooks. 



2. In aquaria watch the caddis- 

 worms in portable cases drag 

 their lumbering houses about. 

 See them retreat inside when 

 disturbed, and see them come 

 out again. Some may be seen 

 feeding on the plants present. 



3. Pick up one of the larger cases 

 containing an active larva, and 



drive the larva forward out of its case by poking a 

 match stick into the case at the rear. Put the larva, 

 naked, into the water and observe what a helpless 

 creature it is when deprived of its proper shelter. 

 4. If you have at hand the living larvae in cases of the 

 form shown in figure 30, or any other similar large 

 form, drive the larvae out of one case, and put it and 

 another larva in a dish of water with a single case, and 

 watch them strive for the possession of that case. 



Fig. 30. — The portable cases 

 of two species of caddis worms 

 (from Lloyd). 



