3o8 NATURAL HISTORY OF AQUATIC INSECTS CH. 







Ephemera there, though we should expect to find 

 them heaped together by the thousand. 



" The larva of Polymitarcys rarely swims free in the 

 water ; it has a burrow excavated in the earthy bank 

 of the river. From the level of the water for two or 

 three feet downwards the bank is everywhere drilled 

 with holes a quarter of an inch or less in diameter. 

 The holes take for the most part a horizontal direc- 

 tion. The passage returns upon itself to a second 

 outlet close to the first, as may be seen by slicing a 

 clod of the earth horizontally, when a U-shaped 

 burrow is exposed, the two limbs being separated 

 only by a slight partition of earth, which is often 

 broken down. The larva can therefore enter or leave 

 its burrow without being obliged to creep backwards. 

 Earth of the consistence of clay or marl is best suited 

 to the purpose ; gravel cannot be made to answer. 

 The lining of the burrows is much finer than the 

 surrounding earth, and appears to be laid down in an 

 even layer by the larva. The burrow is proportioned 

 to the size of its inhabitant ; a full-sized one is more 

 than a quarter of an inch in diameter, and over two 

 inches long, measured from one end to the other 

 along the curve. In such a burrow the larva is freely 

 exposed to the water, while protected from the 

 attacks of Fishes. Its food consists of earth, from 

 which it removes by digestion all nutritive matter. 



" I suppose that the larval stage occupies two years, 

 and that in the last few months of the second year 

 signs of wings appear ; at this time half-grown larvae, 

 destined to manure in a subsequent season, are 

 abundant. 



