CHAPTER XIV 



ORDER PLECOPTERA* 



The Stone-Flies 



The members of this order have four membranous wings. In some 

 genera the branches of the principal veins are reduced in number and 

 there are comparatively few cross-veins; in others, accessory veins are 

 developed and there are many cross-veins; in most genera the hind wings 

 are much larger than the fore wings, and are folded in plaits and lie 

 upon the abdomen when at rest. The mouth-parts are of the chewing 

 type of structure, but are frequently vestigial in the adidt. The cerci are 

 usually long and many-jointed. The metamorphosis is incomplete. 



Members of this order are common insects in the vicinity of rapid 

 streams and on wave-washed rocky shores of lakes ; but they attract 

 Httle attention on account of their inconspicuous colors and secretive 

 habits. They are called stone-flies because the immature forms are 

 very abundant under stones in the beds of streams. 



In the adults the body is depressed, elongate, and with the sides 

 nearly parallel (Fig. 374). 

 The prothorax is large. The 

 antennse are long, tapering, 

 and many-jointed. The 

 mouth-parts are usually 

 greatly reduced. In some 

 genera the mandibles are al- 

 most membranous, but in 

 others they are firm and 

 toothed, being well fitted 

 for biting. The maxillas 

 exhibit variations in the 

 degree of their reduction 

 similar to those shown by 

 the mandibles. The maxil- 

 lary palpi are five-jointed. 

 The labial palpi are three- 

 jointed. The legs are widely 

 separated, except the fore 

 legs in the Pteronarcidge ; 

 the tarsi are three-jointed. The hind wings are a little shorter than 

 the fore wings, but usually, owing to the expansion of the anal area, 

 they are considerably larger than the fore wings ; in a few genera the 

 hind wings are smaller than the fore wings ; in some species the wings 

 of the male are greatly reduced in size, and in others the males are 

 wingless. When at rest, the wings are folded in plaits and lie upon the 



*Plecoptera: plecos (ttX^koj), plaited; pteron {trTepbv), a wing. 



(325) 



374. — A stone-fly, Pteronarcys dorsata. 



