INSECTA : NEUROPTERA 



313 



Change 

 of Habitat. "5*™®' 



segment and one pair on the last segment of the tail. These 

 " creepers " are carnivorous, feeding on smaller aquatic larvae; 

 their mouth-parts are therefore well developed. This stage 

 endures for two or three years. 



When the time has 

 the nymph leaves 

 the water, climbing on to 

 some projecting rock or plant. The 

 skin swells and splits over the thorax, 

 and then the body is withdrawn from 

 it. The wings expand, and after a 

 few hours the tissues have become 

 dry and firm, and the insect flies off, 

 generally, however, remaining close to 

 its former habitat. It does not feed, 

 and only lives a few days. 



The Willow-fly has a 



fly^(N^o^). ^^''y ^i"*^!*"^ life-history 

 and structure, but the 

 two long processes at the end of the 

 body, though present in the larva, are 

 lost at the last moult. The separa- 

 tion of the bases of the two pairs of 

 wings is very marked in this genus. 



Fig. 234.— Larva of Peria 

 liicavjdata. 



Family 4 : Sialidab (the Alder-flies or Humpbacks) 



This family differs from the three so far considered in 

 having a " complete " metamorphosis, i.e. one with a quiescent 

 pupal stage. There are four membranous wings, the difierenee 

 in size of the two pairs being but slight. They are held over 

 the back obliquely, meeting in a ridge over the middle line ; 

 the veining is fairly simple and conspicuous. The head 

 bears long antennae. The larvae of the Alder- flies are 

 aquatic, but there are other members of the same family — 

 the Snake-flies — which have terrestrial larvae. 



The Common Alder-fly (Sialis lutaria). 



These flies can be readily recognised by their long black 

 antennae and darkly veined, dusky wings, the upper pair of 

 which folds over the lower pair when at rest, the hinder part 



