EPHEMERIDA 75 



The eggs of mayflies are laid on or in the water. Either the female 

 alights at intervals on the water to wash off the eggs or she cieeps down 

 into the water to lay her eggs upon the undersides of stones. In either 

 case the eggs finally rest in the water and hatch there into the nymphs 

 which always live in the water. The nymphs breathe by means of tra- 

 cheal gills which are usually situated along each side of the abdomen. 

 They are usually active and live on bits of plant food found in the 

 water. Some burrow in the bottom silt, others climb actively over green 

 vegetation in the water, while others live in swiftly flowing water where 

 they cling closely to submerged logs and stones. 



With many species of mayflies there is great uniformity in the date 

 of maturing of the individuals. Thus immense swarms of them will 

 leave the water at about the same time, and in the course of a few days 

 pass away, this being the only appearance of the species until another 

 generation has been developed. The great swarms of "lakeflies," 

 Ephemera simulans, which appear along our northern lakes about the 

 third week of July, afford good illustration of this peculiarity. 



Family Ephemeridje 



The Mayflies 



The order Ephemerida includes a single family, the Ephemeridae; 

 the characteristics of this family, therefore, are those of the order, which 

 are given above. 



The appearance and habits of the mayflies are certainly well known 

 by those who live in the vicinity of streams, ponds, or lakes. 



In river or lake towns, during the warm evenings of late spring or 

 early summer, the electric lights or street lamps are often darkened by 

 myriads of insects that dash against them, and the pavements are made 

 slippery by their dead bodies which have been trampled under foot. 

 They are not the ordinary night-flying moths: if an individual of the 

 thousands that cling to the posts and buildings in the vicinity of the 

 light be examined, it will prove to be a delicate creature with dainty, 

 trembling wings and two or three long, thread-like organs on the end of 

 its body; the body itself is so transparent 

 that the blood within can be seen pulsating. 

 The front wings are large and finely netted, 

 and the hind wings are small or absent (Fig. 

 123). So fragile are these pale beings that 

 they seem like phantoms rather than real 

 fig 12? —Canis i nsec ts. No wonder that poets have sung of 

 a two-winged May- them as the creatures that live only a day. 

 It is true that their winged existence lasts 

 often only a day or even a few hours; but they have an- fig. 124. — Nymph 

 other life, of which the poet knows nothing. Down on the of Mayfly - 

 bottom of a stream, feeding on mud, water-plants, or small insects, 

 lives a little nymph with delicate, fringed gills along its sides and two or 

 three long, many-jointed, and often feathery appendages on the end of the 

 body (Fig. 124). It has strong legs and can both walk and swim. After 

 about the ninth molt — there may be twenty molts in all — there appear 

 on its thorax four little sacs which are the beginnings of wings; with each 



