140 NATURE STUDY AND AGRICULTURE 



water tigers. The method of breathing may be seen by 

 the children. At the hind end of the body are two little 

 projections with openings or breathing pores in them. 

 Watch the larvae curl the end of the body upward and 

 stick these projections above the surface. When the larva 

 is ready to change to a pupa it crawls upon the bank and 

 makes a small cell in the ground. It remains here three 

 weeks and then changes to a beetle. Some time should be 

 given to discussion of the value of the cybister as a mos- 

 quito destroyer. 



The water scavenger beetle may be studied in much the 

 same way as the cybister. A comparative study of the 

 two will make a profitable lesson. The children will dis- 

 cover that the scavenger uses its legs differentiy while 

 swimming, that it rests with its head out of the water, that 

 it takes a film of air on the under side of the body, and that 

 it feeds upon decaying vegetable matter as well as insects. 

 The eggs of these beetles may be found floating upon the 

 water in large, white, irregular cocoons. The cocoons are 

 easily identified by a curious handlelike stem on one side. 

 There are from fifty to one hundred eggs in each cocoon. 



THE CABBAGE BUTTERFLY.— Seventh Grade 



General Problem. — Where do the cabbage worms come 

 from, and what may be done to lessen their numbers? 



Ask the children to bring in cabbage leaves that have 

 worms on them, or pass to the school garden and examine 

 the cabbage plants there. Where did the worms come 

 from ? The children have probably seen the white cabbage 

 butterfly flying around the cabbage patch alighting now 



