CLASSIFICATION AND DESCEIPTION OF COMMON INSECTS 



99 



Dragon-flies and Damsel-flies (Odonataj.- — These insects are also 

 well known. They are rapid fliers over bodies of water, feeding on 

 flies and mosquitoes. The nymphs live at the 

 bottom of ponds and streams. They have 

 long legs, and are flat and spiny. Dragon-flies 

 hold their wings horizontally when at rest, and 

 the nymphs have rectal respiration; while the 

 damsel-flies hold their wings vertically when at 

 rest, and the nymphs have three caudal tra- 

 cheal gills (Fig. 56). 



Caddice-flies (Trichoptera). — The larvae of 

 these insects are known as caddice-worms, and 

 live in water within protecting cases of fine 

 gravel, leaves, sticks, stalks or small shells, 

 •fastened together by threads of silk. They 

 crawl about carrying their cases with them. 

 When full-grown they change to pupcB within 

 the cases and at length emerge as four-winged 

 flies. During summer immense numbers are 

 attracted to lights at night. The wings are 

 hairy, and, at rest, are held like a roof over the back, 

 usually laid on water plants. 



Fig. 55. — Nymph of 

 s t o n e-fi y {Pteronarcys 

 regalis). 



The eggs are 



Fig. 56. 



-Dragon-fly {Libellula pulchella). Last nymphal skin and wings. Slightly 

 reduced. {After Folsom.) 



Dobson-flies, Lace-wings, Ant-lions (Neuroptera). — Dobson-flies 

 are large insects with prominent biting mouth-parts and wings. Their 

 larvae live under stones in swift streams, and have rather conspicuous 

 tracheal gills. They become full-grown in about three years. 



