MAYFLIES, DUNS AND SPINNERS 231 



the general appearance of a mayfly nymph, and the 

 student will notice that it is furnished with powerful 

 mandibles and forelegs somewhat similar to those of 

 the mole cricket. These are used for digging and 

 making the tubular galleries in the clay, mud, or sandy 

 grit on the bed of the river. The life of a mayfly 

 from the egg to the perfect insect is computed at 

 from two to three years. 



The nymphs in this division have all parts of their 



bodies wide and flat. They 

 Flat nymphs. are not shaped so as to be 



able to dig, and naturally do 

 not hide in burrows like the immature mayflies. They 

 are not rapid in their Fig. 39. March Brown Nymph x 4 



movements, and the 

 small depth of their 

 bodies is eminently 

 fitted to their scheme 

 of life as they pass 

 the whole of the 

 nymphal stage cling- 

 ing to the underside 

 of large stones. Their 

 life from egg to imago 

 is generally believed 

 to extend to one year, 

 but some species are 

 believed to grow more 

 rapidly and produce 

 two broods in the 



