AQUATIC INSECTS 



row in the muddy shallows of lakes and rivers, sometimes in 

 the banks of upland bog-streams. They can be distinguished 

 by the rounded, shelflike piece on the front of the head 

 (Fig. 154). They are the largest of the mayflies, fullgrown 

 n^^mphs being from one and one-half to two inches long 

 (PL XIII). They eat the rich diatom ooze through which 

 they plough their way. Sloping banks are sometimes mined 

 by them, and the openings of the burrows with mayfly tails 

 hanging from them can often be seen along stream margins 

 (PI. XIII). If such nymphs are pulled out and thrown down 

 onto the mud they will burrow in again with the speed of 

 ground-moles. 



Pig. 155. — Adult male of Hexagenia hilineata, 

 in its favorite position; one of the large mayflies 

 which swarm over lakes. 



These are the mayflies which fly in such great numbers be- 

 neath lights and on lake shores (Fig. 155). There are many 

 stories and records of their abundance. According to Dr. 

 F. H. Krecker's observations made at Cedar Point, Lake 

 Erie, "when a brood is at its height it is a very common 

 occurrence to find piles of the insects three or four feet square 

 and six to eight inches deep under electric lights. At a 

 neighboring amusement resort several carts were required 

 each morning to haul away the dead insects." 



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