Aquatic Insects 107 



bottom, the May-fly submerging herself 

 for the purpose. The larvae are her- 

 bivorous, feeding upon algae and other 

 plant tissues. Some species burrow in 

 the mud, while others creep about among 

 the weeds. When the time is due for 

 the adult May-fly to appear the larva 

 rises to the surface and there rests ; the 

 skin of the back splits and the winged 

 insect makes its way out and takes 

 flight. This winged stage is not the true 

 adult, but is what is known as the sub- 

 imago, for another casting of the skin 

 has to take place before the final stage 

 is reached. May-flies are noted for the 

 shortness of their lives in the winged 

 state ; some live only a few hours, while 

 others may endure for twenty-four or, in 

 a few instances, a little more than a day. 

 The aquatic life of the larva is as rela- 

 tively long as that of the adult is short, 

 for certain species spend three years in 

 the water before reaching maturity. 



