CHAPTER IX 

 ORDER EPHEMERIDA * 



The Mayflies 



The members of this order have delicate membranous wings, triangular in 

 outline and with many cross-veins and usually extra longitudinal veins; 

 the hind wings are smaller than the fore wings and are sometimes wanting. 

 The mouth-parts of the adidts are vestigial; those of the nymphs are fitted for 

 chewing. The metamorphosis is incomplete. 



The name of this order is from the Greek word ephemeros, lasting but 

 a day. It was given to these insects on account of the shortness of their 



lives after reaching the adult state. The mayflies 

 are easily distinguished from other net-winged 

 insects by the peculiar shape of the wings and the 

 relative sizes of the two pairs (Fig. 122). 



The mouth-parts are nearly wanting, as these 

 insects eat nothing in the adult state; the an- 

 tennas are very small ; the abdomen is long, soft, 

 and terminated by two or three many-jointed, 

 thread-like appendages. 



Mayflies exhibit a remarkable peculiarity in 

 their development. After the insect leaves the 

 water and has apparently assumed the adult form, 

 that is, after the wings have become fully ex- 

 panded, it molts again. These are the only insects 

 that molt after they have attained functional 

 wings. The term subimago is applied to the 

 instar between the nymph and the final form of 

 the insect, the imago. With some species the 

 fig. 122. — Mayfly. duration of the subimago stage is only a few 



minutes ; the insect molts on leaving the water ; flies a short distance ; and 

 molts again. In others this stage lasts twenty-four hours or more 



What is spoken of as the brief or ephemeral life of the mayflies is 

 true only of their existence in the adult state. Strictly speaking, the 

 mayflies are long-lived insects. A few species pass through their life- 

 cycle in a few weeks in midsummer; but as a rule one, two or three 

 years are required for the development of a generation. The greater part 

 of this time is passed, however, beneath the surface of the water as a 

 nymph and after the insect emerges and assumes the adult form its 

 existence is very brief. With many species the individuals leave the 

 water, molt twice, mate, lay their eggs and die in the course of an evening 

 or early morning. In the case of other species the adults may live several 

 days; yet the lives of these are short compared with those of other in- 

 sects. 



* EphemeYida, Ephemera: ephemeron (k^rinepov), a Mayfly. 

 74 



