98 ECONOMIC ENTOMOLOGY 



DD. Abdomen without external lateral gills. 



E. X-ower lip strong extensile and furnished with a pair of 

 opposable hooks; abdomen terminated by 3 leaf-like 

 tracheal gills, or with 5 spine-like appendages. — 

 Odonata. 

 EE. Lower lip not extensile and without hooks; caudal 

 filaments and antennae long and slender; thorax with 

 3 pairs of tracheal giWs.—Plecoptera. 



On account, however, of their common occurrence the economic 

 entomologist should know a little at least regarding their habits and 

 life-history. 



Stone-flies (Plecoptera). — The nymphs hve under stones in swift 

 streams, are flattish, and have tracheal gills, long legs, cerci and 



Fig. 54. 



-An adult stone-fly {Pteronarcys regalis). 

 Folsom). 



Slightly reduced. {After 



antennae. The adults are greyish and have prominent wings. The 

 hind wings are the larger and when at rest are folded under the front 

 ones. The larvae furnish food for fishes (Figs. 54 and 55). 



May-flies (Ephemerida). — May-flies are well-known insects, being 

 attracted to lights in immense numbers in early summer. They have 

 large delicate wings and 2 or 3 long caudal filaments. The fore wings 

 are much larger than the hind ones. The nymphs Hve at the bottoms of 

 bodies of water, and have long legs, caudal filaments and prominent 

 tracheal gills. They_mature in i to 3 years, and furnish abundant 

 food for fishes. 



