HOW TO KNOW THE IMMATURE INSECTS 



7a. Tracheal gills (plate, feather, tassel or finger- 

 like) usually occur on abdomen or thorax (none 

 in some small Plecoptera); 2 or 3, long, many 

 segmented tails present at caudal end of abdo- 

 men; aquatic life. Fig. 56 8 



7b. Abdomen or thorax without tracheal gills and 

 without long segmented tail-like filaments at 

 caudal end; short cerci may exist 9 



The presence of gills as well as their type is more pjg. 55 /^ Mayfly 

 easily determined if the specimen is floated in water Tracheaf |ms.^ *^^ 

 or preservative. They are often so fine and may lie so close to the 

 insect as to not be readily apparent in dry specimens. The function 

 of the gills, of course, is to extract oxygen from the water. The gills 

 are extensions of the tracheal tubes. 



8a. Tracheal gills (plate, feather, or tail-like) located on lateral mar- 

 gins of abdominal tergites only; 3 tails (in some family only 2), 

 fringed with rather long setae, occur at caudal end; tarsi possess 

 1 claw. Fig. 57 Order EPHEMEROPTERA page 62 



Fig. 57. a, Heptogenia 



sp. 



Hexagenia bilineata Say 



About 1,500 species of Mayflies ore 

 described. Their naiads are aquatic 

 and long lived, in some cases, this per- 

 iod is believed to occupy three years. 

 Between the naiad and the imago, there 

 is a subimago stage which differs from 

 the mature imago in its duller appear- 

 ance and its somewhat translucent 

 wings which are usually margined by 

 prominent fringes of hairs. They are 

 essentially herbivorous, feeding upon 

 fragments of the plant tissues. Certain 

 forms, however, are believed to be car- 

 nivorous. 



33 



