Mayflies 



205 



The mayflies (order Ephemerida) are all aquatic. 

 They live in all fresh waters, being adapted to the 



greatest diversity of situations. 

 The adults are fragile insects, hav- 

 ing long fore legs that are habit- 

 ually stretched far forward, and 

 two or three long tails that are 

 extended from the tip of the body 

 backward. The wings are corru- 

 gated and fan like, but not folded, 

 and are held vertically in repose. 

 The hind wings are small and incon- 

 spicuous . The antennae are minute 

 and setaceous. The head is con- 

 tracted below and the mouth parts 

 are rudimentary. Thus, many 

 characters serve to distinguish the 

 mayflies from other insects and 

 make their group one of the easiest 

 to recognize. 



Mayflies are peculiar also, in 

 their metamorphosis. They 

 undergo a moult after the assump- 

 tion of the adult form. They 

 transform usually at the surface 

 of the water, and, leaving the 

 cast-off nymphal skin floating, fly 

 away to the trees . Body and wings 

 are then clothed in a thin pellicle 

 of dull grayish and usually pilose 

 skin, which is retained during a 

 short period of quiescence. During 

 this period (which lasts but a few 

 minutes in Casnis and its allies, 

 but which in the larger forms lasts 

 they are known as subimagos or 



Fig. 112. An adult may- 

 fly, Siphlonurus alterna- 

 tus. 



one or two days) 



